Note: A version of this article appears in the Spring 2019 issue of Building Stone Magazine.

We are living in the age of information. In the palms of our hands, we can tap into an enormous realm of facts, opinions, advertisements, and educational materials. However, because information is so easy to access and share, plenty of not-so-great material gets widely circulated, too. Our challenge is to sort fact from fiction, to educate ourselves, and guide designers, architects, and customers through the melee.

The countertop industry is a big one, offering billions of dollars in annual sales in the United States alone. Naturally, competition is fierce as various companies vie for attention and make bold claims to lure customers. Quartz countertop manufacturers are working hard to influence the marketplace, and they are doing so with big promises and lofty assertions. As with all information, it’s important to pause and reflect on the validity of these statements so that we can make informed choices.

What’s In a Name?

Companies that manufacture quartz countertops have been very clever with their naming. The word “quartz” represents one of Earth’s most abundant minerals. One well-known brand of quartz surfaces says that their product is “pure natural quartz.” The phrase admittedly has a nice ring to it. But how accurate is it?

Geologically speaking, a manmade quartz countertop is not pure natural quartz. The only thing that fits that criterion is quartzite, which truly is pure natural quartz. Manufactured quartz surfaces are mostly quartz, but they are not purely quartz. Depending on the brand and the color, manmade quartz surfaces are 70% to 93% quartz sand or aggregate, mixed with polyester resin, ethenylbenzene (also known as styrene), pigments, and other additives.

Is Engineered Quartz the Same as Natural Stone?

I believe another area of confusion arises when quartz manufacturers refer to their products as natural stone. For example, one paragraph of a quartz company’s website begins: “All natural stone surfaces, including [company name]….” This type of phrasing is prevalent throughout the company’s marketing materials. In other examples, they say that they sell the world’s “most beautiful and innovative natural stone surfaces,” they “offer the world’s finest natural stone countertops,” and they describe their products as “stone slabs.”

From my perspective as a geologist and a professional admirer of rocks, I can easily appreciate the attempt to align a manmade product with a natural one. We can all agree that natural stone is awesome. But manmade quartz isn’t natural stone. It’s a bit brazen to say that it is. 

For the record, natural stone is both naturally occurring and made out of stone. Granite, limestone, quartzite, and marble are all natural stones. They form in nature, and only in nature. They are made of minerals, and only of minerals. Feldspar, quartz, hornblende, hematite, garnet, calcite, muscovite: these are the ingredients in nature’s pallet. You’ll find no polyester resin on a seafloor, nor ethenylbenzene in a magma chamber—thank goodness.

Will the Real Mont Blanc Please Stand Up?

Mont Blanc quartzite (right) a natural stone, is often imitated by manufactured quartz producers. Notice the inherent difference of one manufacturer’s Mont Blanc (left) and a second company’s Montblanc (center) as manufactured quartz product offerings compared to its natural counterpart. Photos supplied by Slabworks of Montana and Triton Stone.

Stroll through a retailer that sells paint, tile, stone, or anything else that comes in colors and flavors, and you’ll encounter an amusing selection of names for colorways. Customers face a staggering array of choices as they work through the details on new construction or remodels, and at times the decisions can feel paralyzing. Should your clients opt for Cloud White or Dune White for their trim color? Should the grout be Bleached Wood or Urban Putty?

As for the countertop, should they choose Mont Blanc, Mont Blanc, or perhaps Montblanc? Continuing the theme of copying natural stone, several quartz companies have usurped individual stone names and applied the exact same label to their manmade products. The original Mont Blanc is a genuine natural stone: a white quartzite with light grey layering. Mont Blanc is also the name of a slightly speckled pale grey manufactured product of one quartz producer. Montblanc is also a white and grey “marble-look” from a second quartz producer.

Some quartz product names intentionally evoke natural stone, such as this manufactured quartz offering called Calcutta Borghini (inset image), factory created and similarly named to compete with Calacatta Borghini marble, shown installed in this kitchen. Photos courtesy of Triton Stone.

This practice is widespread. Some quartz product names intentionally evoke natural stone: Capri Limestone, Charcoal Soapstone, Onyx Carrara, Calacatta Nuvo. Other cases are even bolder, taking the identical names from well-known stones and applying them to manmade versions. Super White, Taj Mahal, Emperador, Thassos, Nuage, and Statuario are all popular, prestigious natural stone, but they are also the names of synthetic countertops. How about Piatra Grey versus Pietra Grey? Do you know which one is real stone and which is an imposter?

I suspect that most in our industry can empathize with the potentially confusing choice designers and customers need to make. The best we can do is to help guide clients toward options that meet their needs, while providing education about different types of products. But when companies deliberately muddy the water and intentionally confuse their customers, it makes life harder for all of us.

Granite Comes From the Earth

Naming aside, what are the practical differences between manmade quartz products and genuine natural stone? Let’s start by looking at how each one is formed.

 A perpetually popular natural stone for countertops is granite, an igneous rock that was once molten magma. Magma occurs throughout the Earth’s crust: under volcanoes, along seams between tectonic plates, and in hotspots.

The texture of granite sheds light on its past. Magma that cools relatively quickly will have small and uniform crystals. Deep magmas cool more slowly. In the process they grow beautiful, large minerals with complex shapes that are evocative of their internal atomic geometry. Granites with super large minerals, called pegmatites, form when there is some water mixed with the magma, which spurs minerals to take shape more readily.

In all cases, the rock turns from liquid to solid over a span of thousands to millions of years, and takes shape miles deep within the Earth’s crust. These inexorably slow geologic processes forge a stone that is dense, durable, and will far outlast our lifetimes. Thanks to variations in the composition of the magma, granite comes in a span of all-natural colors, from nearly white, to coppery brown, to deep grey and black. Patterns range from mild to wild, with aesthetic variations to suit all styles and tastes. Each piece of natural stone is unique and each bears the mark of a particular time and place in our planet’s history.

Manmade Quartz Comes From a Mold

Manufactured quartz slabs are composed of three main ingredients: particles of mineral quartz, resins, and pigments. The quartz particles can vary in size from about 5 millimeters down to less than half a millimeter. Polyester resin binds the mineral pieces together. In some cases, the resin is mixed uniformly through the slab, and in other cases there are visible areas of resin, depending on the design. The same is true of pigments; some designs are the same color all the way through, while others have ribbons or accents of different hues, which are often meant to imitate the naturally occurring patterns in natural stone.

Manufactured quartz slabs are made by blending the ingredients, then pouring the mixture into a mold. Different manufacturers use different processes, but some combination of vibration, compaction, heat, and a vacuum are applied to cure the slabs from a slurry to a solid.

Testing the Hardness of Quartz Slabs

The website of a major quartz manufacturer makes this statement about the durability of its product:

  “[Company name] is much harder than granite or marble making it more durable. That means [company brand] is less likely to scratch, chip, or stain for years of worry-free service.”

Before we jump into a fact-check on hardness, it’s worth pausing to point out that hardness only relates to a surface’s resistance to being scratched. Hardness has little to do with chipping and nothing to do with staining.

Areas with pools of resin are often the softest part of a manufactured quartz surface. On this sample of Cambria Shirebrook, the resin is lightly scratched by a tool with a Mohs hardness of 6. Image courtesy of Karin Kirk.

Is quartz surfacing much harder than granite? This is straightforward to verify using metal picks calibrated to different hardness on Mohs scale. In test cases where the sample contained large particles of mineral quartz, the individual quartz grains yielded a hardness of 7. The “matrix” material around the larger particles were generally 6 to 7, with some areas between 5 and 6. Larger pools of resin were between 5 and 6. On colors where the particles are uniform and fine-grained, the hardness fell in the range of 6 to 7.

How does that compare to granite? Mineral quartz has a hardness of 7. Feldspar has a hardness of 6 to 6.5. These two minerals make up somewhere between 100% and 90% of a standard commercial granite. Other typical minerals in granite could include hornblende (hardness 5-6), pyroxene (hardness 5-6), biotite (hardness 2.5-3), and garnet (hardness 6.5-8.5).

I analyzed samples from several different quartz manufacturers. The Cambria samples I tested were similar to, or slightly softer than granite. Are they “much harder?” No.

This Caeasarstone sample is scratched by a metal tool that has a Mohs hardness of 6, and this result was repeated on several samples and colors. Therefore the hardness of these samples is less than 6. Caesarstone lists the hardness of their product as 6.5 to 7. Image courtesy of Karin Kirk.

Looking at other brands yielded similar findings. The fine-grained matrix on Caesarstone colors such as Buttermilk, Lagos Blue, and Pebble had a hardness of between 5 and 6, while larger, individual quartz particles in coarse-grained varieties were 7. Pental samples were largely between 6 and 7, with a few spots in the 5-6 range. LG Viatera samples came in right around 6 or slightly less. Silestone Nebula colors were also between 5 and 6.

These results make sense. Particles of quartz are a hardness of 7, regardless of whether they are in a natural stone or a manmade composite. Polyester filler and binder materials are softer than quartz, which is reflected in the softer values in those areas of the slab.

 “Dancing a Mighty Fine Line”

Fabricator Dave Scott has been making countertops for 25 years. He works in quartz, natural stone, and sintered ceramic materials and he appreciates the advantages of each. His shop, Slabworks of Montana, serves high-end clients near Big Sky and Yellowstone Club ski resorts, as well as more typical homeowners in the Bozeman area.

 “I’m not anti-quartz,” he explained, “but I’m just not a fan of some of their marketing.” In his experience, the biggest drawback of manufactured quartz is the way it can be damaged by heat. “I’ve replaced enough of them; I know,” he said wryly. Electric frying pans and slow cookers are some of the biggest culprits, he added, which can cause quartz surfaces to crack or scorch. Over the course of his career, Scott has seen numerous failures with cook top cutouts, more so than with natural stone slabs.

Scott noted that many quartz manufacturers list the upper end of the proportion of mineral quartz in their products, but they don’t often cite the lower ranges. “They range from the low 80s up to 93% at the top,” he said, while explaining that the solid colors typically have a lower percentage of quartz minerals.

When it comes to the way manufactured quartz companies call their products natural stone, Scott voiced some concerns. “Either you are [natural stone] or you’re not,” he quipped, adding that the claims of manmade quartz companies are “dancing a mighty fine line.”

“They’re trying to compare themselves to natural stone,” said Scott. He motioned out the window to the rows of granite, quartzite, and marble in the yard, adorned by recent snowfall, and continued emphatically, “But these are unique, God-made pieces of art for us to enjoy.”

And therein lies the essential difference between purely natural products versus engineered lookalikes. There can be no doubt that real stone is a product of the Earth, created by geology, God, or whichever combination you prefer.  Natural stones are natural, abundant, and fundamental parts of our planet. They bring life and energy into our homes and public spaces and are unquestionably authentic. Amid the confusion wrought by marketing strategies, perhaps the most useful conclusion lies in the age-old adage: Imitation is the sincerest form of flattery.

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Perusing slab yards is always an adventure. At first, it’s novel and exciting. Granite and marble and limestone, oh my! But aisle upon aisle of stone can trigger shopper’s overload. How can you tell them apart? Which one is right for you? Is Brazilian granite superior to Indian granite? And what to make of the enticing labels? Is Verde Butterfly Extra going to make your life better than Verde Butterfly Non-Extra?

Take a deep breath. We have answers for you. While subjective things like shades of off-white (ecru vs. cream?), stone names, and design trends can be dizzying, there is one tool that can reliably help you cut through the confusion. I’m talking about science, my friend.

Aside from the obvious fact that science is super cool and sexy, there’s a real advantage to this approach: you will learn for yourself how stones perform. By experimenting on stone samples, you’ll not only gather key bits of information, but you’ll also gain confidence in the real-world attributes of various stones. There’s nothing like your own personal experiences to reassure you that your stone is going to tick all the boxes for your situation.

Match the properties to the purpose

The first step is to assess your primary needs. A hardworking kitchen countertop in a family home might require durability as the top priority. A bathroom floor might favor texture and grip. A stone patio in Wisconsin needs to resist splitting, while the countertop at a bank will have to resist fingerprints and oils.

If possible, make a list of the properties that are most important to you before you head to the showrooms. That way, you can zero in on the types of stone that fit your criteria, and avoid the potential heartbreak of falling in love with slabs that don’t match your requirements.

Assemble your toolkit

We scientists love our gear, so here’s a list of items you can use to investigate stone samples:

• Glass tile
• Pocket knife
• Small bottle of lemon juice or vinegar
• Spray bottle of water
• Cloth for wiping up water or acid
• Magnifying glass (or use the magnifier function on your phone)
• Camera and notebook to document your findings

Obtaining samples

As you evaluate various types of stone, be sure to explain to the sales staff that you’d like to do a little “sciencing” on some samples. Many dealers are happy to provide samples of stones that you’re considering. This is a smart practice because an educated customer is likely a satisfied customer. Fabrication shops are another source of potential samples, and the scrap bins offer a treasure trove of stones to satisfy your geologic curiosities.

Ideally, industry professionals will appreciate your desire to be as informed as possible, and can accommodate customers who want to ‘test drive’ stones before committing to a purchase. Who knows, perhaps salespeople will be similarly curious about a stone’s performance, and can help guide your investigations. In an age where information is passed along so easily, sometimes without regard for context or validity, it’s in everyone’s best interest to engage in our very own, science-based fact checking.

Hardness

In geology-speak, the hardness of a stone is its resistance to being scratched. Hardness is not the same thing as strength or durability, which we’ll get to in a moment.

Hardness is important when it comes to things like using metal utensils on your countertop, or scuffing muddy shoes across a stone floor. Of all the properties, hardness is the simplest to evaluate. Using a glass tile, check your stone sample to check to see if the stone scratches the glass.

A few tips:

• Use a sharp corner of the stone.
• Press hard, but be careful not to press so hard that you risk breaking the glass. Set the glass on a tabletop to do the test, rather than holding it in your hand.
• There will almost always be a mark on the glass, but it’s not always an actual scratch. Wipe off any stone dust, then feel the scratch with your fingernail. Sometimes the stone simply ‘draws’ on the glass, and sometimes it scratches it. Get a little nerdy and investigate what’s really happening.

Another way to check the hardness of a stone is to use the tip of a knife blade to try to scratch the stone. One advantage of this method is you can examine individual minerals and check out different parts of the stone.

Stones that are harder than glass or a knife blade are likely to stand up well to wear and tear. Softer stones are still perfectly useful, even in high-wear areas, but it depends on your own preferences and needs.

Durability

How well a stone stands up to splitting, crumbling, and cracking are all part of its durability. This is harder to measure because it’s more subtle and subjective. Here are a few categories to investigate.

• Splitting. Many types of stone are layered. Use a broken (not sawn) edge and see if you can peel apart the layers. How strong are the layers? This is especially useful for slate and schist, which have pronounced layering. The large “flashy” areas of layered mica can add stunning beauty to the overall appearance, but can flake off if near the surface.

• Grains. All rocks are made of minerals, but in some cases those minerals are not stuck together too well. Investigate the edges of a stone and see if it’s possible to loosen or remove any grains. Use the tip of a pocketknife and have at it. In most cases, this test is a reassuring one. It’s not easy to pry grains out of a solid rock, and trying to do so will help you recognize the strength of your stone.

• Cracks and fissures. A naturally occurring break in a stone slab is called a fissure, and if it’s human caused (during fabrication or handling, for example), then it’s considered a crack. Fissures in stone are a perfectly normal occurrence. All kinds of geologic stresses can cause a stone to fracture, and in many cases, these areas heal themselves with minerals carried along by groundwater. But once the stone is out of the ground, that process will no longer take place, of course. Weaknesses in the stone are mostly a concern during fabrication, transportation, and installation. Once the stone is in place, it’s not likely to break as long as it’s well supported underneath. That said, it’s wise to investigate any irregularities in a stone’s surface, regardless of if they are natural or not. Can you feel the edge of a fracture on the slab’s surface? If not, then the cracks/fissure is unlikely to be a problem. Does a fracture run all the way through the stone? Will it be near edges or overhangs? If so, then it’s a good idea to trim that area off the slab during fabrication.

Acid resistance

Acids can affect stones that contain calcite or dolomite: marble, dolomitic marble, limestone, travertine, or onyx. Acid sensitivity is another quality that can seem like a mystery, but is easy to measure. Use lemon juice or vinegar, puddle it on the stone, and let it sit for several minutes. Wipe off the acid, then look at the stone at a low angle. Etching looks like a dull area on the surface of the stone. When a stone etches, a tiny amount of the stone dissolves in the acid. This won’t affect the strength or longevity of the stone, but it does make a visual mark. Sealing does not prevent etching, but occasional re-polishing or re-honing will remove etch marks.

Some stones etch quickly and easily. Others take longer to show effects, and etch marks are less noticeable when they do occur. If you love marble but are concerned about etching, you can opt for a honed finish, which often makes etch marks less visible compared to a polished finish. Etching is less of a concern in areas where acids are not used, or for people who don’t aspire to perfection in their homes. So, acid reactions are not necessarily a deal breaker. But a little experimenting will tell you how your potential stone reacts, and will help guide your decision.

An important rule of thumb is that granite, quartzite, and soapstone do not contain acid sensitive minerals. If you want to be sure to avoid etching, then seek these types of stone and do the tests to be sure the stone is classified correctly.

One last clarification on this subject is that we’re talking about everyday acids like citrus, vinegar, wine, or tomato juice. Powerful acids like rust removers and toilet bowl cleaners are much more potent and should be kept away from all types of natural stone.

Staining/porosity

Everybody loves strawberries. But we don’t want to be perpetually reminded of them with a bright pink berry stain on the kitchen island. Staining is linked to porosity—in other words, how much open space exists within the solid matrix of the stone. Thankfully, the high pressures that bind rocks into solid forms tend to squeeze away most of the pore spaces. But different stones have been subjected to different amounts of squeezing, and thus, porosity varies among stone types.

Testing for porosity can be done a few different ways. You can put some water on the surface of an unsealed stone and watch what happens. Does it soak right in? If so, that’s a stone with high porosity. Does the water bead up, and wipe away cleanly? Then you’ve got a tightly compacted, low porosity stone on your hands. If the water doesn’t visibly soak in, but leaves behind a shadow or a damp spot when wiped away, then the stone has intermediate porosity.

If you want to get a little fancier, you can put stone pieces edge-wise in a shallow pan of water and see if water wicks up into the stone. Details about porosity tests are described in the Deep Dive Into the Properties of Quartzite.

You can also check for porosity using cooking oil, but bear in mind that oils will often leave a residue on the surface of the stone even if the oil doesn’t soak into the stone’s pores. After letting oil sit on the stone, scrub it with soapy water, rinse it, and then let it dry completely. At that point you can evaluate the oil’s effect on the stone.

Impregnating sealers should be used with porous stones, and a sealer will reduce or slow the rate of absorption to allow you to clean it before a stain becomes a problem. But that’s your second line of defense. Your best bet is to use the test to find a stone with a lower porosity in the first place, if that’s what your desired usage requires.

Why a basic granite satisfies most measures

There’s a reason why granite is such a popular type of natural stone. It scores well in all the diagnostic tests. It’s made of quartz and feldspar, which are harder than glass. It doesn’t split into layers, and the minerals are held tightly together in an interlocking, jigsaw-like arrangement. None of the minerals in granite are affected by everyday household acids. Granite is also beautiful, and thanks to the wonders of geology, comes in a stunning range of colors and patterns. It’s a win for its properties and its good looks.

It’s often said that knowledge is power—which is certainly applicable when it comes to gathering information and learning about any kind of big purchase. In the case of natural stone, you’ll not only learn about hardness, etching, and porosity, but you’ll also gain insights about geology and the planet. In the end, not only will that help you understand the traits of your natural stone, but it will help you appreciate its origins, too.

	Basic supplies for a casual geology lab.
	Testing the hardness of sandstone with a glass tile. The sandstone is harder than glass.
	Testing the hardness of marble with the tip of a pocketknife. The marble is softer than the knife.
	Ordinary white vinegar is useful for checking for acid sensitivity.
	This soapstone has such low porosity that liquids puddle up on top of the stone surface, without soaking in at all.
	Testing the porosity of sandstones and quartzites in a shallow pan of water for 15 minutes.
	Testing the porosity of sandstones and quartzites in a shallow pan of water with pink food coloring.

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Bookmatched Azul Imperiale.

The same idea – minus the salami – applies to marble stone slabs, as well. When two neighboring slabs are ‘opened up’ and polished on the surfaces that were facing each other, the pattern on each stone will be virtually identical, except they will be mirror images of each other. These twin slabs can then be arranged along a common edge to produce a stunning, kaleidoscopic pattern. Bookmatched slabs sometimes look like butterflies, or Rorschach (inkblot) tests, or many other fanciful shapes. Bar none, bookmatched slabs are one of the most dramatic and impressive ways to use natural stone.

Best places for bookmatching

A pair of bookmatched slabs commands a lot of attention. For maximum effect, these statement pieces should be used where there’s ample room to accommodate a large expanse of stone, like a big kitchen island, a conference room table, a wall, or an oversized shower. If you have a large area to cover, bookmatching is a handy way to ensure that the pattern runs fluidly from one piece to the next.

It’s not a great idea to cram a bookmatched pattern into a surface that’s interrupted by corners, cutouts, and appliances. The bigger the expanse, the greater the impact. That said, a bookmatched pattern need not be limited to full slabs. Smaller pieces of bookmatched stone are often used in flooring tile or backsplashes.

Variations on the bookmatch

Diamond matched marble wall. Photo courtesy of United Marble Fabricators.

If the standard two-slab bookmatch is somehow insufficient to satisfy your design tastes, you can take it up a notch with diamond-matching (also called quad-matching). This arrangement uses four pieces of stone, and is so named because it commonly produces a diamond-shaped pattern.

Bookmatched pieces needn’t be all on the same plane, either. A vertical slab on a wall can be mated to its twin on a horizontal countertop or bathtub surround, for example.  This gives an immersive effect, as if you are sitting inside of a vast block of stone.

Another variation on the theme is called vein-matching (or slip-matching), where the key visual elements of the slabs are matched to flow across seams and produce a continuous pattern. Vein-matching is commonly seen on ‘waterfall’ arrangements, where a horizontal countertop joins a vertical panel of stone that runs from the countertop down to the floor, or from the countertop up to the backsplash. Vein match in these instances is typically preferred over bookmatch.

Considerations when hunting for slabs

At the quarry, large blocks of stone are removed from the ground, then shipped to a facility for processing. Here, the big blocks are sliced into slabs. When the slabs are all polished on the same side, it’s called “consecutive” polishing (also called “sequential” polishing). These slabs are usually numbered so you can purchase neighboring slabs if needed.

To create a near-perfectly matched pattern, the surfaces of two neighboring slabs have to be processed so the surfaces that were facing each other are both polished. This operation is usually done when the slabs are cut from the block, and is not commonly done at a fabricator’s shop. In some cases it’s possible to convert sequential slabs to bookmatched slabs by polishing the back side of one of the slabs. But it’s less hassle and more reliable if the slabs were originally processed and polished with bookmatching in mind.

Because bookmatched slabs generally originate at the sawyer, there can be significant lead time if stone needs to be ordered. Plan ahead and be patient – the wait will be more that worth it.

Bookmatching tends to be more expensive than a standard layout, because in every case two slabs are needed, even if the area to be covered is not that large. And if one slab is lost to breakage or other issues, the entire layout of slabs can be lost due to the irreplaceability of the one slab. The painstaking planning and fabrication required to execute a precise match-up of the pieces may also add to the cost.

Any of the four edges of the slabs can be aligned. Showrooms often have bookmatched slabs on display like an open book, but keep in mind you can swap them left to right – or top to bottom – if you want. Each arrangement will yield a different pattern. You can mock up different variations to visualize the possible outcomes. The images below were created in PowerPoint by importing a single picture of a slab, copying it, making a mirror image of it, then dragging and rotating the two shapes to make different designs. For those who prefer a hands-on approach, you can print two photographs of the slab and fiddle with various layouts. (Warning: Regardless of the method, this is a mesmerizing and addictive process!)

While these graphics are electronically generated and show perfect mirror images, such perfection is not attainable in actual stone fabrication due to variation within the stone. Even in neighboring slabs, the patterns can vary over short distances, depending on the nature of the pattern and the direction of the grain. So, it is wise to expect a certain amount of non-uniformity amongst sibling slabs.

Since bookmatching requires two pieces of stone to be placed exactly next to each other, the edges of the slabs that are destined to be joined together have to be in near-perfect condition. Any chips, cracks, or awkward areas that are trimmed off of one of the slabs must also be removed from its mate.

Patterns: The good, the bad, and the whaaat?

Bookmatched Fusion granite.

The natural colors and patterns in stone will almost look amplified when presented in the mirror-image arrangement of a bookmatched pair. A certain amount of movement is required to create a visually interesting effect, but an overly complex stone can cause sensory overload. Stones with soft hues and flowing movement, like marble, will create a beautiful look that’s not too jarring. Vivid slabs with bright colors and high-contrast patterns are not for the faint of heart, but offer an unforgettable statement.

It’s practically inevitable that you’ll see images in the adjoining stones. Maybe it will look like a beautiful flower or a snowy owl. Or… maybe you’ll see the face of a malevolent goblin, or, heaven forbid, something resembling the, ummm, human anatomy? Once seen, these forms can’t be unseen; they will greet you every time you walk in the room. So take your time and carefully examine the potential designs and shapes you’ll end up with once the stones are cut and assembled.

Craftsmanship and communication

A downside to bookmatching is that there is little room for error in the fabrication and installation. The trimming and alignment of the slabs has to be spot-on. For this reason, careful communication with your fabricator is absolutely essential. Don’t assume you both know which way the slabs will be oriented and which parts will be cut off. Make sure that the fabricator has plenty of experience with bookmatched slabs, and that you share the exact same vision for the final product.

The best way to visualize and communicate the plans is with is with photographic images, mockups, and a dry-lay of the stone panels prior to installation. Many fabricators have the ability to import images of the slabs into computer software and then decide where each cut and seam will go. It’s imperative to go through this step together, and to sign off on the final plan. Neither the customer nor the fabricator wants any surprises on installation day, so if there was ever a time to be extra-careful in the planning phase, this is it.

Bookmatching is natural stone at its best

The coolest thing about bookmatching is that it takes the patterns of geology, which are plenty awesome on their own, and boosts them to an almost supernatural aesthetic. If you feel there’s no artist that can rival Mother Nature, then bookmatching might be for you. Pairing your own imagination with the inherent beauty of the Earth can forge a phenomenal result.

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This article touches on 13 different types of natural stone, with links to each type to explore further.

Organizing natural stones into categories

You learned this in 8th grade: Geologic categories of stone

Geologists, like all scientists, love to put things in categories. We group rocks by the process that formed them. Did a rock erupt from a fiery volcano, or take shape in a placid river bed?

Making more useful categories: Grouping stone by their properties

I’ll admit that geologic categories aren’t all that helpful for the way natural stones are used. Instead, we can group stones by the properties that matter to us, like how they hold up in the places we use them.

Here’s an overview of rock types sorted by hardness and their ability to withstand an onslaught of marinara sauce.

Note the empty category of hard stones that are damaged by acids. It turns out that hard minerals also tend to be unaffected by household acids. That’s just a coincidence of mineral chemistry, but it’s convenient for those looking for a hard, resistant natural surface.

When we talk about acid resistance, we’re referring to things like vinegar or citrus. Strong acids like oven cleaner and some bathroom cleaners will damage almost any stone, so keep those away from your stone, or better yet, use less toxic means to clean your home.

Relationships between different types of stone

In the world of geology, all stones are related to each other. Over deep spans of time, any rock can turn into a whole new rock if it gets melted, squeezed, uplifted, or eroded. In fact, that’s exactly what’s been happening all through Earth’s history. Understanding the relationships between different stones can make it easier to see why some share similar traits. It also helps you appreciate the events that gave rise to all those beautiful slabs in the showrooms.

Sedimentary rocks turn into metamorphic ones

Limestone forms in shallow, warm oceans and coral-rich beaches. It’s made of shells, shell fragments, and dissolved shells. Limestone can get buried and heated to taffy-like consistency, wherein it turns to marble. Both stones are made of the same mineral – calcite – but in marble’s case the calcite grains have been crystallized together, making the stone less porous. Marble’s distinctive grey streaks are clay layers from the original limestone that got heated and swirled.

The relationship between sandstone and quartzite follows a similar theme. Sand grains gather on beaches, sand dunes, and riverbanks. Layers of sand get buried and pressed together, forming sandstone. If sandstone gets shoved down deep and compressed even further, the sand grains fuse together to become quartzite. As described in the Deep Dive Into Quartzite article, this process is a gradual one. This means there are many gradations of sandstone and quartzite, ranging from highly porous sandstone to bombproof crystalline quartzite. The more deeply a stone is buried, the more tightly compacted it will get. The porosity of a stone translates into its ability to shrug off stains, and this is something that buyers can evaluate as they shop for different stones.

Bluestone is a variety of sandstone. It formed as rivers flowed off a former mountain range along the eastern seaboard. As 400,000,000 year-old rivers wound their way through the landscape, they left behind pockets of sandstone in Pennsylvania and southern New York. Because the sandy deposits occurred in small, scattered areas, the quarries were small, too, setting the stage for generations of family-run quarrying operations throughout the region.

Dialing up the heat on slate, schist, and gneiss

This trio of rocks shows what happens if you crank up the thermostat on a stone. The predecessor to all of these stones is shale, which is compressed clay and is decidedly un-sexy. But add a little heat and pressure and those unremarkable clay particles start to grow and strengthen and the rock turns into slate. Unlike shale, slate is durable – and is workable into tiles, shingles, and of course, old-school blackboards.

If the stone gets hotter, the clay particles morph into mica and the rock takes on a subtle sheen. This is called phyllite, but in commercial terms phyllite is usually sold as slate. More heat begets even larger mica grains, and the stone becomes schist, which is known for its glittery look. Schists with small mica grains are preferable to stones with large chunks of mica, because the latter can be weak and literally flaky.

Adding even more heat and pressure will make the stone separate into bands of light and dark minerals. Striped or banded patterns are the hallmark of gneiss. The patterns can be calm or bold, straight or swirled. For commercial purposes, gneiss is usually classified as granite, because it’s made of the same minerals, and shares similar properties and colors.

If the stone gets hotter still, it will start to melt. In some slabs of gneiss you can see melted blobs of quartz, showing the stone was right on the edge of becoming liquid again. If the whole thing melts, then you’ll end up with granite, an igneous rock.

The many colors of granite

Granite means many things. It’s a catch-all category that’s often used to describe any hard, crystalline stone. In geology, granite is one specific thing: an igneous rock that is coarse-grained and overall light-colored. But in the parlance of the natural stone industry, the definition of granite is expanded to include all igneous rocks, as well as many metamorphic rocks like gneiss and schist.

Geologists classify igneous rocks by the size of the crystals and the types of minerals. And while you will definitely sound smart if you casually inquire if your local slab yard has any quartz monzonite or granodiorite, that’s not necessary. Most igneous rocks are quite similar to each other, despite their different colors and patterns. We can just stick to calling them all granite. (Just please don’t tell my geology friends I said this!)

Basalt is one type of igneous rock that is famous for erupting out of volcanoes, like the spectacular lava flows from Kilauea we saw last spring and summer. Basalt also makes up the entire ocean crust (which itself is volcanic, betcha didn’t know that!) and forms oceanic islands like Hawaii and Iceland.

Solid rock from liquid water

Onyx and travertine are variations of the same stone. They come about from mineral-laden water, like you’d find at the mouth of a hot spring. Both are made of calcite, the same mineral that’s in limestone and marble. Travertine has a lacy pattern from the way the water flows in little rivulets away from the mouth of a hot spring. Onyx can form from either hot or cool water, and is less porous than travertine. Onyx is beloved for its smooth layers and gem-like colors that are especially glorious when backlit.

Last but not least: The oddball stone that doesn’t fit into any categories

It’s true with people and it’s true with stones, too. Not everyone fits into a tidy category. Soapstone, for instance, is basically nothing like other rocks. It manages to be soft, yet dense. You can scratch it with your fingernail, but you can’t stain it or burn it, no matter how careless you are. Soapstone is more like a family of stones rather than one specific thing, but it is cool stuff, and I bet it will surprise you.

Geologists and natural stone aficionados agree

Natural stone offers a lot to love—there’s zero doubt about that. Take a moment to learn about the history and characteristics of your favorite stone, and I bet you’ll appreciate it even more.

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Soapstone enjoys a cult-like fan base: “I love the organic-ness of it,” writes one devotee on Houzz. But it’s not for everyone. “I find these photos rather sobering,” laments another commenter after viewing images of the patina that soapstone can acquire.

Yes, Soapstone is Soft

“All stones have benefits and disadvantages,” says Anthony Lacour of M. Teixeira. “There’s no such thing as a perfect surface.”

As the branch manager at M. Teixeira’s Denver office, Lacour has been working with this iconic stone for a dozen years. He suggests the best way to get a feel for soapstone’s hardness is to experience it personally. “Let people test for themselves,” he says.

Hardness of most commercial soapstones ranges from 1 to 4, but Lacour has found that the exact Mohs number is not as important as just getting a sense for it. “Use a fingernail and a key as your hardness indicators,” he advises.

Soapstone’s softness might be a dealbreaker for some—it comes down to knowing yourself and recognizing if a scratch in the stone is going to ruin your day, or how long it will take you to forgive a family member who accidentally drops a frying pan on the countertop.

Lacour explains the upside: “The good thing is that you can fix it yourself.”

A fresh coat of mineral oil will render small scratches invisible. Larger marks can be removed with sandpaper. Lacour recommends 120-220 grit for most scratches; if you prefer a shinier finish, you can follow up with 400-500 grit. Then re-oil the surface to restore the luster, and you’re all set.

Even a gouge is fixable—it can be filled with a mixture of stone chips and epoxy. This can be tackled by a professional or by a seasoned DIYer.

Steve Schrenk is the digital media director for Polycor, and he has worked with stone as a sculptor, fabricator, and designer. He describes soapstone as “very user friendly for self-repair,” noting that soapstone appeals to the type of person who “likes to roll up their sleeves and do it themselves.”

A Houzz commenter sums it up best, “What I love love love the most about soapstone: If you are a DIYer at heart (or a control freak, like I am), then the self-maintenance of the counter is just wonderful.”

And Now for the Good News: Soapstone’s Superpowers

Once you’ve come to terms with soapstone’s softness, you can revel in its strengths. By and large, the stone is remarkably resistant to staining or damage from acids. The density of the stone makes it practically impervious. That smoldering casserole you left in the oven while binge-watching Better Call Saul? Put that right there on the stone, thank you very much.

These superpowers were not bestowed on soapstone by any magical process. It comes down to the properties of the minerals in soapstone. Soapstone’s primary ingredient, talc, is chemically inert, which is why soapstone is generally unaffected by acids and alkalines. Talc is also hydrophobic, meaning it quite literally repels water.

The mineral magnesite is another major component of soapstone, and it has the ability to retain heat. The properties of magnesite allow soapstone to work so well as an insulator or a fireplace. The stone is capable of absorbing heat and then slowly radiating it off, providing the long, sustained warmth so appreciated in cold climates. Lastly, soapstone is a dense arrangement of small minerals, with minimal pore space that might allow water to seep in. Low porosity means that soapstone will not absorb liquids nor harbor bacteria—a perk for the germaphobes among us.

Schrenk sums up the yin and yang of soapstone: “People tend to latch on to the scratching aspect of soapstone,” he says. But they may be “missing out on some of the other aspects of the stone” that make it so appealing.

Soapstone’s Quirky Geology

Soapstone is an unusual type of metamorphic rock. Most metamorphic rocks are heated and squished versions of their former selves. Limestone becomes marble. Sandstone turns to quartzite. But soapstone doesn’t abide that simple recipe. Soapstone comes about from a series of chemical reactions that take place deep underground. Hot groundwater carries dissolved minerals from one rock to another, allowing a mingling of ingredients that begets entirely new minerals. In some cases, soapstone is a derivative of dolomite or dolomitic marble (like Super White). In others, soapstone comes from ultra-deep, ultra-dense rocks from Earth’s mantle. In this latter case, serpentine is also formed, and hence, soapstone and serpentine can often be found side-by-side in a quarry or outcrop.

Soapstone’s signature soapiness comes from the mineral talc. Talc is a member of the mica family, and is made up of thin flakes. The flakes are held together by a very weak type of bond, which allows the layers to easily slide against each other, giving the stone a slippery feel.

Talc is the softest mineral on Earth, with a hardness value of 1. Soapstone always contains some talc, but the amount varies, and therefore so does the overall hardness of soapstone. Stones with high talc content are called steatite, and are useful for carving. Commercial soapstone slabs generally have 30% to 50% talc, with the remainder of the stone being chlorite, magnesite, amphibole, and other minerals. In general, the lower the talc content, the greater the hardness.

Geologically, soapstone is a family of stones rather than one specific thing. There’s broad variation in the types of minerals present and their proportions. This is all the more reason to thoroughly investigate potential stones and to work with reputable dealers and fabricators.

If a stone looks sort of like soapstone but can’t be easily scratched with a pocketknife, it’s likely serpentine rather than soapstone. Virginia Mist and Jet Mist are granites that resemble soapstones, but are much harder. When in doubt, use the diagram below and read up on how to tell green stones apart.

Evaluating the Hardness of Various Soapstones

Soapstone really is different from most other types of stone. What better way to explore this than to try a battery of tests and see how it performs. M. Teixeira sells a sample kit of various soapstones to allow customers to experience a range of soapstone colors, textures, and hardnesses. I used a set of Mohs hardness picks to get up close and personal with the hardness of 12 soapstones. I tried to scratch different minerals in the stone with picks of various hardness values. I also used my fingernail and a pocketknife so that I could compare common items with Mohs numbers.

The results varied depending on how much talc the stone contained and what other minerals were present. While all the samples fell into a range between 1 and 4, they were different from one another, and even a single stone could have different hardness values in different places.

A summary of soapstone hardness is given in the table below, and the stones are arranged roughly from softer to harder.

Testing Acid Resistance

After I checked out the hardness of the 12 soapstones, I moved on to acid tests. I put a 10% solution of hydrochloric acid on every sample, and also used standard white vinegar to check for etching. I left the acids there for at least a half hour, before scrubbing the stones with soap and water and inspecting them for damage.

Several stones had a slight bubbling reaction with hydrochloric acid. This is expected because soapstone sometimes has calcite veins, and/or it can contain magnesite, which will have a very subtle reaction to acid. Interestingly though, 11 of the 12 stones showed no damage, etching, or staining from the hydrochloric acid, even though the acid initially looked like it had stained some of the stones. But it washed away and left the stone unaffected. Similarly, vinegar left no mark whatsoever on 11 of the 12 stones.

One stone, Stormy Black, showed a faint etch mark where vinegar was left puddled up for several hours, and the hydrochloric acid left a stippled white pattern on the black stone when left for an hour. This stone appears to be somewhat susceptible to acids, and likely has more magnesite than the other samples. The dark color and fine texture of Stormy Black may also make the changes appear more noticeable.

Aside from that, the other 11 samples looked brand “new” (while appreciating the fact that they are indeed several million years old!).

Oiling or Waxing Enhances the Finish of Soapstone

Soapstone can have two distinct looks, depending on the finish. It can be left untreated and will attain a soft grey color and a matte finish. Or, the surface can be oiled or waxed, which will darken the color and impart a satiny luster. “You get multiple looks from the same stone,” says Lacour.

To oil, or not to oil: that is a frequent dilemma among soapstone owners. Light oil like mineral oil is easy to wipe on but will fade fairly quickly. Wax can also be used as a surface treatment. It requires more effort to apply, but it lasts longer. An oil/wax blend strikes a happy medium between the two.

One needn’t agonize over this decision, because it’s always reversible. Thanks to soapstone’s density, the oil simply sits on the surface. It doesn’t penetrate the stone. If you change your mind and decide you don’t like the oiled look of your soapstone, you can scrub most of it off right away, or simply wait for it to disappear on its own.

One minor caveat to the oiled vs. naked finish is the color of the seams. During installation, the epoxy in the seams will be dyed to match the stone. But since the color of the stone depends on whether it’s oiled or not, you could end up with a slight mismatch. When in doubt, savvy soapstone owners suggest going with a lighter color in the seams, because the seam can be darkened more easily than it can be made lighter.

Best Uses for Soapstone

Around the world, soapstone has been shaped into cooking pots, utensils, vessels, and sculptures for thousands of years. Soapstone’s workability made it especially useful during the Bronze Age, when molds were carved out of soapstone and filled with molten metal.

Today, soapstone is a beloved material for wood stoves and fireplaces. At the Bridger Bowl ski area in frigid Montana, a soapstone stove is the central feature in a slopeside warming hut. The stove is thoughtfully placed in the middle of the room, beckoning to visitors and easing the woes of chilly children. Once heated, the stone gives off warmth long after the fire goes out. Even after sitting idle all night long, the soapstone is still warm the next morning.

Soapstone is well known as a worktop in laboratories, where its chemical inertness and heat resistance allow it to withstand all manner of abuses.

These same traits make soapstone an enviable material in the kitchen, where it’s commonly used for countertops, islands, or sinks. Unlike many types of natural stone, soapstone cannot be polished to a glossy shine. Instead, it has a soft, warm glow and rounded edges that help a space feel comfortable rather than imposing. “Our kitchen looks loved! It looks lived in! People who eat together and tell stories and make each other laugh and spill their drinks live here!” writes a fan of soapstone on Houzz.

Both Lacour and Schrenk agree that soapstone fills a distinct niche in the industry. Soapstone’s grey tones and honed finish are on-trend nowadays, but soapstone won’t ever go out of style. While some stones draw attention to themselves, “soapstone’s subtle colors plays well with other elements of design,” explains Schrenk. “It fits a 100 year old building or new construction,” observes Lacour. Schrenk echoes the same sentiment: “It’s modern use of a traditional material.”

Alberene – Virginia’s Soapstone Quarry

Not far from Charlottesville, Virginia sits a large soapstone deposit and an active quarry that dates back to 1883. Over the years, Alberene soapstone was destined for a variety of applications, ranging from industrial uses of talc in tires and roof shingles, to practical objects like sinks, bed warmers, and griddles. Polycor purchased the Alberene quarry 5 years ago, and they’ve been pleasantly surprised by the enduring popularity of soapstone. “It’s surpassed everyone’s expectations,” says Schrenk. Alberene’s most popular soapstone is called Church Hill, literally named because of a hilltop church near the quarry. Nowadays, the quarry mostly produces slabs destined to become countertops, tiles, pavers, treads, wall caps, and fireplace inserts. “There’s a huge surge right now, especially for countertops,” says Schrenk.

The uptick in demand is easy to appreciate. Alberene soapstone is local, natural, and has “a tactile quality” that customers are drawn to, explains Schrenk. He finds that once customers learn what sets soapstone apart from other stones, “they sing its praises.”

Is Soapstone Right for You?

Choosing stone is always a personal decision, but even more so with soapstone. Only you know your situation and squeamishness, and Lacour’s advice to test the stone yourself rings true. Thankfully, soapstone dealers typically provide samples for customers to work with, so you can bring pieces home and try out your own scratching, etching, and staining tests. (You can also take our Stone Personality quiz.)

This bit of online advice nails it: “I’m looking forward to the aging and patina. But it would be sad if someone who wasn’t up for it spent a lot of money and had their heart broken.”

As with every material, the more you learn about it and the better you understand your own needs, the easier it will be to narrow down your choices.

If you’re curious about soapstone, spend some time interacting with it and see what you think. I found myself falling more in love with the samples the more I played with them. Another Houzz commenter said it best: “To those of you considering soapstone, do not be afraid!”

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