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|DWYER MARBLE & STONE SUPPLY • DESIGN NEWSLETTER • Vol. 1, Issue 1||click to call: 248.476.4944|
Getting to Know Your White Stones
by Karin Kirk
White Stone Countertops | Which One Is Right For You?
White kitchens and bathrooms are perpetually popular. White countertops brighten your workspace, add cheer to a room, and cooperate with any color palette or design style. No wonder white stones are constantly in demand.
Geologically speaking, pure white rocks are rare. While there are many white minerals, such as quartz, feldspar, and calcite, they don't always assemble themselves into a perfectly white rock. That said, there are plenty of mostly white or nearly white stones that offer possibilities for bringing texture and geologic interest to your white countertop.
A timeless white marble is what many of us envision when we imagine a serene white kitchen or bath. Beautiful marbles have been in use for centuries, and with good reason. They are gorgeous and they never go out of style.
Yule marble, quarried in Colorado, was used in the Jefferson Memorial.
White marbles are usually swirled with darker colors. These veins are remnants of thin layers of clay within the original limestone, which have been transformed into flowing patterns as the rock was heated and compressed. This metamorphic process squeezes and stretches the rock, producing the wavy movement that characterizes marble and makes us swoon over it. Meanwhile, the original limestone recrystallizes into marble, making it less porous and more dense.
The colors of the veins offer styling cues that can compliment a kitchen or bathroom design. The caramel hues of Calacatta Gold pair well with warm wood tones. Marbles with cool grey veining, such as Montclair Danby, are a good match for contemporary accents like nickel or stainless fixtures. Some marbles have a green hue, caused by the mineral serpentine.
In rare circumstances, geologic conditions lead to an exceptionally pure limestone with no clay or sand mixed in. If a pure limestone undergoes metamorphism, a pure white marble is produced. One example is the Yule Marble quarried in Marble, Colorado, which is 99.5% pure calcite. This stone was used to build the Jefferson Memorial in Washington, DC. Thassos marble is another example of a pure white stone that offers a sleek, uncluttered aesthetic.
A marble breccia adds a dramatic flair to a classic look. Breccia is a geologic term for a rock that is composed of angular fragments. These rocks were subjected to folding and shearing stresses that caused the original limestone to fracture. Mineral-rich groundwater glued the fragments back together while also lending some color contrast to the rock. Rest assured that a breccia is not weakened because it was once broken into pieces. The pieces have been bonded back together at great depths in the Earth's crust and have been perfectly intact for tens of millions of years or more. The stone is just as solid as any other.
Super White is an example of a dolomitic marble breccia. It has subtle colors, but a dynamic texture. Perfect for making a statement without overwhelming your design.
All marble shares similar properties. Most marble resists staining, particularly when sealed. Marble is around 3.5 on Mohs hardness scale, meaning it's softer than knives and cookware. Perhaps the Achilles' heel of marble is its tendency to etch when exposed to acids like lemon juice or vinegar. Many people consider marble to be a "living surface" that develops patina and character with use. On the other hand, some of us prefer a stone that won't show any wear.
Many homeowners face a dilemma as they pine for the classic beauty of marble but worry about its maintenance in a household with small children or a less-than-cooperative spouse. This is precisely why quartzite has become a superstar of natural stone. Quartzite shares the light coloration and the soft pattern of marble, but it contains entirely different minerals. Genuine quartzite is made of quartz, which is 7 on Mohs scale and will not etch from typical acids you'd use in your kitchen. Sounds perfect, right? The downside is the price. You can expect to pay more for quartzite for a few reasons. Quartzite is not as abundant as marble and it is considerably more difficult to fabricate. Quartzite's hardness and density can be a challenge for cutting tools, so be sure your fabricator has experience with real quartzite.
With its best-of-both-worlds abilities, quartzite is in high demand. However, some stones that are labeled as quartzite are actually marble. To further confound the issue, the unfortunate tem of "soft quartzite" has emerged to try to account for so-called quartzites that don't have the properties of real quartzite. This mystery can be easily solved by doing a few diagnostic tests on the stone.
Like marble, quartzite colors can be warm like Taj Mahal, or cool like White Macaubus. For that matter quartzite can tinged with vivid blue, orange, or green.
Granulite is a geologic name for a class of metamorphic rocks formed under particularly high temperatures. The rock became chemically altered, but it did not completely melt. In the parlance of the decorative stone industry, these stones would simply be called granite. But it's more fun to use their real name so you can sound extra smart while cruising the aisles of the slab yard. Popular examples of granulite are River White, Colonial White, or Bianco Romano. Many granulites are white to light grey or light cream color. They are made mostly of feldspar and quartz, with minor amounts of garnets and other darker minerals. Some granulites have a gentle linear or wavy pattern, while others are evenly speckled.
Compared to most granites, these stones can be slightly more porous. They require regular sealing to prevent staining. Granulite has the same hardness as other granites, around 6 on Mohs hardness scale.
Granulites are an excellent choice for a durable, trouble-free stone that won't break the bank. They have just enough movement and personality to be interesting, but their light, even coloration allows them to play well with other colors or patterns.
Pegmatites are a special type of granite that have huge crystals. They have a bold texture that is primarily white, cream, or light grey. Pegmatites form in the same manner as regular granite: from liquid magma that slowly cooled underneath the surface of the Earth. But pegmatites have extra-large crystals because water circulated through the magma chamber, accelerating the process of crystal formation.
Delicatus White granite.
Patagonia granite is one that will stop you in your tracks in the showroom. The iceberg-sized minerals are geologically fascinating. In some cases, a single mineral crystal can be several feet long. The porcelain-white crystals are feldspar, while the light grey ones are quartz. Rectangular-shaped, black minerals are hornblende. These are the same minerals that are in normal granite, only supersized!
If you want something with a little less drama, consider a pegmatite with crystals that are large, but not huge, such as Mystic Spring, Alaska White, or Delicatus. These stones are predominantly white, but they have some pattern and movement too.
Whether you're drawn to a strongly patterned pegmatite or a demure marble, you've got many possibilities for white stones. Next time you find yourself wandering the stone showroom, take a moment for a closer look at these geologic beauties.
Quartzite Need Not be a Confusing Stone
Quartzite has been causing confusion within the natural stone industry. Some people say it etches. Some say it doesn't. Sometimes you hear it's a hybrid between marble and granite. Yet, others report that it's harder than granite. Which is it? Why are there such conflicting reports about quartzite?
The problem with quartzite stems from the fact that it is commonly mislabeled. Some quartzite is the real deal, but sometimes marble or dolomitic marble are labeled as quartzite. Because each of these stones behaves differently, people might understandably conclude that quartzite is variable. But it isn't; quartzite has very consistent properties. Unfortunately, it has variable labeling.
The good news is that this problem has an easy solution. You can use basic diagnostic tests to cut through the confusion and learn for yourself which stones are genuine quartzite and which ones are not. Better yet, you can steer your customers toward a stone with properties that are a good fit for their needs, and you won't risk having a customer who is disappointed about the performance of their stone.
The key points of this document are to describe the simple diagnostic tests that can be used to distinguish quartzite from marble, and to encourage their use to clear up confusion about quartzite.
What is Quartzite?
Quartzite is a metamorphic rock made almost entirely of the mineral quartz. Quartzite begins its geologic life as sand grains, perhaps on a beach, desert dune, or riverbed. Over time, the sand grains become compressed and stuck together to form sandstone. If the sandstone gets buried ever more deeply underneath layers of rocks, it gets hotter and more compressed. With enough heat and pressure, the sand grains lose their original shape and fuse to their neighbors, forming a dense, durable rock. The process is similar to individual snowflakes merging into solid, glacial ice.
Quartzite is usually white or light-colored because quartz sand is light colored. Additional minerals carried by groundwater can impart hues of green, blue, or ion-red. Van Gogh and Azul Macaubas quartzites are examples of vivid coloring.
Regardless of color, quartzite is made primarily of one thing: quartz. That's helpful because the hardness and acid resistance of quartz set it apart from the minerals in marble. (Note — The mineral quartz should not be confused with the brands of manufactured countertop materials commonly referred to as "quartz surfacing" which contain crushed quartz with a resin binder.)
Properties of Quartzite Hardness
One of the appeals of quartzite is its hardness and durability. Not only does this make for a tough stone, but it also makes it easy to tell quartzite from the imposters. Quartz is 7 on Mohs hardness scale. It's nearly twice as hard as glass and harder than a knife blade. These things are easy to test with a sample of stone.
Resistance to Acids
Etching is caused by acids dissolving small areas on the surface of a slab of stone. While this process does not harm a stone, it does blemish the surface. One of the appeals of quartzite is that it does not etch from acids like lemon juice or vinegar. If a rock labeled as quartzite becomes etched from acid, then it is mislabeled. Marble and dolomitic marble, on the other hand, will etch from these acids. Dolomitic marble etches slightly more slowly than regular marble. But quartzite will not etch at all from normal kitchen acids.
Quartzite has a range of porosities. Some, like Taj Mahal or Sea Pearl, have been highly metamorphosed and the minerals are bonded together tightly. White Macaubas and Calacatta Macaubas have been exposed to less intense pressure, so these stones are more porous and will benefit from sealing.
Simple Diagnostic Tests for Quartzite
There are simple tests that are used to distinguish quartzite from marble. By doing these tests, you don't have to rely on a stone's labeling or what you have heard about it. You can figure out a stone's identity for yourself. You may discover that a stone is incorrectly labeled, in which case the label should be changed. It's worthwhile to learn as much as you can about any stone you are selling.
Test 1: The Glass Test
The Glass Scratch Test.
© 2017 Karen Kirk for MIA + BSI
What the results mean:
Continue your investigation by doing the etching test as described below.
What if there is no broken edge to use, such as a full slab with epoxied edges?
The Knife Blade Test.
© 2017 Karen Kirk for MIA + BSI
Test 2: The Etching Test
Quartzite will not etch when exposed to typical household acids, but marble will. Customers can try an etching test with lemon juice or vinegar. But the standard geologic test for acid reaction calls for a 5% to 10% solution of hydrochloric acid. Many fabrication shops already have muriatic acid on hand, which is nearly the same as hydrochloric acid. However, the dilution of the acid is important. A very strong acid will dissolve stones more readily than a diluted one, and it won't help distinguish between different types of stone. Thus, the correct dilution is important. The simplest way to ensure the proper concentration is to order a 5% or 10% dilution of hydrochloric acid from a laboratory supply company. Store the acid in a dropper bottle, and use it whenever you need to distinguish quartzite from marble.
How to do the acid test:
If you see no bubbles or very subtle bubbles, try the powdered rock acid test:
If you did the acid test on a polished or honed surface, then you can rinse off the stone, dry it, and then inspect the surface for an etch mark. Etching can look like a lighter area, a darker area, or a place where the shiny finish of the stone has become dulled. If the stone bubbled with acid, then you will almost certainly see an etch mark where the acid was. That means the stone is marble. If you didn't observe any bubbles, then you most likely will not find an etch mark. This would confirm that the stone is quartzite and not marble.
The glass test and acid tests are simple to perform, and it is a good practice to use these tests on every stone that is labeled quartzite. Try it on your existing stock. Try in on new batches. Show your colleagues how to do it. The tests are the only way to definitively tell quartzite from marble. In some cases, you may find yourself re-classifying stones that were incorrectly labeled as quartzite. This will help prevent customers from being confused and disappointed by a stone that does not live up to its billing. It is well worth the time to correctly identify your stones, rather than letting incorrectly identified stones create problems for customers.
There is No Such Thing as Soft Quartzite
The unfortunate term "soft quartzite" has emerged to try to explain why a rock that is labeled quartzite is actually not hard and durable like real quartzite. There is no such thing as soft quartzite. There is only one kind of quartzite and it's hard and will not etch. If a stone does not have these properties, then it is not quartzite, regardless of what its label says.
Stones labeled as soft quartzite are most likely marble. The term "soft quartzite" has already gained traction within the industry, but it's a misleading term that should be avoided. With all the misinformation that circulates about quartzite, your staff and your customers will appreciate learning the authentic information about quartzite.
We encourage stone dealers to eliminate the term "soft quartzite" and to instead use the correct categories: marble and quartzite. Categorizing stones accurately will help you give clear and consistent information to your staff and customers.
Things That Do Not Help Distinguish Quartzite from Non-Quartzite
The country of origin, price, or the names of a stone are not reliable indicators of what type of rock you've got. In many cases, it's not even possible to tell marble and quartzite apart visually. Information about a stone's origin is often passed along by word of mouth, which can perpetuate incorrect information. But you can look beyond what you hear about a stone and use the diagnostic tests to find out what it really is.
Quartzite and marble can look very similar, but they have dramatically different properties.This is why testing the stones is the only assured way to tell them apart.
What's the Difference Between Quartzite and Granite?
Granite is a whole separate category of rocks that form from liquid magma. Visually, granite has distinct flecks of darker colors in it, while quartzite has either no dark colors at all, or has subtle, flowing areas of different colors.
Granite and quartzite have similar properties. They are both harder than glass, and neither will be etched by acids. But geologically, they are different classes of rocks and they should be marketed as such.
What's the Difference Between Quartzite and Sandstone?
Quartzite and most sandstones are made of the same mineral — quartz. The difference is in how the minerals are held together. Sandstone is made of sand-sized particles that are held together with mineral cement. Mineral cements are typically silica or calcite that are dissolved in groundwater. As groundwater passes through the sand grains, minerals precipitate out of the water and attach to the sand grains, acting as "glue" that holds the grains together. Some sandstones are porous and loosely cemented (Palomino, Stonewood, Rainbow Teak) while some are tightly cemented (Wild Sea).With quartzite, the grains are fused together with little to no space between each grain. Quartzite does not contain individual sand grains. Instead, the rock is a solid, crystalline mass. Thus, quartzite is much less porous than sandstone.
Potentially Confusing Stones
There are a few stones that can yield conflicting results from the scratch test and the etch test. In some cases, marble will scratch glass. This is because certain marbles contain minor amounts of quartz. This does not mean the stone is a hybrid of marble and quartzite. It is still marble, and should be sold as marble and treated as marble. A few specific examples are discussed below.
Super White May Contain Quartz.
© 2017 Karen Kirk for MIA + BSI
Super White is one of the stones that is frequently caught in the quartzite vs. marble mystery. Most commonly, Super White is dolomitic marble. That means it won't scratch glass and it will etch with acids. Dolomitic marble (CaMgCO3) is slightly slower to etch than regular marble (CaCO3), which can lead people to think that the stone won't etch. But it will still etch.
Some Super White has minor amounts of quartz mixed in with the marble. When doing the glass test with Super White, be sure to test a few different areas to get a sense for the overall rock. You may find that there are some areas that scratch glass and others that don't. This small amount of quartz does not change the overall performance of the stone. It is still dolomitic marble and needs to be treated as such.
This is another stone that can be a bit confusing. Fantasy Brown is made of layers that have been folded and squeezed together. Some of the layers are marble, and some are quartzite. It's best to treat this rock as marble. Do the glass or acid tests on each layer individually and you will be able to tell which layers are marble and which are quartzite.
The Diagnostic Tests are Your Friend
The confusion surrounding quartzite and marble is understandable. The stones look alike, and the abundance of conflicting information further muddies the water. Thankfully, the properties of quartzite make it easy to distinguish from other stones. Exploring the properties of different stones can give you confidence to know what stone you have. So try the tests and see what you find - there is no substitute for firsthand knowledge.
© MIA + BSI