Dec 28th 2020 / General Stone Care
Marble for Countertops
What is Marble?
You may have already considered using marble for countertops based on its look and feel but how much do you know about the substance itself? When it comes to shopping for kitchen surfaces, marble can be defined widely. It's essentially any dimensional stone that is dolomitic, serpentine-based, and calcareous. Once it has been polished and labeled as marble, then that's what it is.
With regards to petrology, however, it's much more narrowly defined. In this instance, marble must be a metamorphic calcareous rock. This means that it has taken on a new form that is distinct from its original form. Compare this to sedentary rocks that stay the same.
Marble begins life as limestone, which is coarse and fossiliferous. After being exposed to high pressure and high temperature, the rock physically changes to become marble. Although limestone and marble are chemically the same substance, they are different rocks as a result of this metamorphosis. It has been crystallized and polished, making marble for countertops.
How Long Does it Take to Create Marble?
It can take up to 250 million years for marble to be formed. However, the metamorphosis that takes it from being limestone to being counter-ready marble only takes around 10 million years. Over this long period, the chemical makeup doesn't change, mostly consisting of calcium carbonate (CaCO3) or dolomite (CaMg(CO3)2).
On some occasions, the chemical makeup may change slightly as surrounding substances are forced into the limestone. This normally happens due to a dramatic event, such as an earthquake. This can lead to marble that has a different appearance, including colors ranging from white or brown to orange or even green.
Compact Limestone: A Commercially Viable Alternative
When it comes to building your countertop, you'll likely browse many so-called marble surfaces that don't fit this exact definition. Instead, shops will sell compact limestone as a perfectly adequate alternative. In the store, this will be advertised as marble for countertops. In fact, this is true in the majority of cases.
The only real difference in geological terms is that the crystallization of compact limestone happened without any metamorphosis. This means that the limestone didn't change physical form but was still able to be polished. For most people, the difference between compact limestone and marble is impossible to discern.
Only a true expert can spot that distinction. The compact limestone is likely to be slightly harder than true marble with smaller crystals. This leads to a deeper polish. Generally, though, you won't be able to tell the difference.
Where Does Marble for Countertops Come from?
You can find incredible marble all over the United States of America. It's largely found in Tennessee, Alabama, and Georgia, but also exists in Vermont. These are considered to be some of the finest marble anywhere in the world.
Outside of these hotspots, you may find some excellent marble in Colorado. Compact limestone is less common because it's not quarried to the same extent as true marble. However, there is plenty of this substance hiding in the Appalachian Mountains.
Green Marble: Not a True Marble
When searching for marble for countertops, you may have come across green marble. It's important to point out that this is also not truly marble, at least from a geological perspective. This does look a lot like other kinds of marble but that's where the similarities end. The chemical composition is completely different. While calcite is the dominant chemical in both marble and compact limestone, it's almost non-existent within green marble.
Instead, green marble is made from silicate minerals. This includes magnesium silicate. This is classified scientifically as being part of the Serpentine Group. Chemically speaking, then, this can hardly be said to be a type of marble, despite the name given to it.
There are a small number of other substances known as green marble. These belong to the scientific classification known as ophicalcite. This is a type of sedentary rock and actually comes in a number of colors, including burgundy. This type of stone gets its color from a high proportion of hematite contained within it. The green ophicalcite is considered a green marble because it contains a tiny proportion of calcite.
What's the Best Serpentinite Green Marble?
Serpentine rocks are classified by scientists as part of the serpentinite group. These make up the great majority of green marbles. If you're looking for green marble for countertops, then you're not alone. This is one of the most popular materials used in American kitchens. Don't settle for anything less than the best quality.
The absolute finest serpentine green marble is found in Vermont. Specifically, it is quarried from Verde Antique. This can be up to 1.5 times as hard as marble and is highly porous. This means that they don't react to acid and so will stand up to heavy usage, no matter how prolific you are in the kitchen.
When installing this green marble from Verde Antique, you have to be careful. During installation, the marble can warp, causing chemical reactions. This can lead to a white efflorescence leaking out of the top of the green marble. This can happen with other types of marble but is a particular problem with this kind.
In order to overcome the potential dangers of installing this specific type of green marble, use a completely solid base. Expert kitchen installers will recommend that you place the green marble tiles on epoxy, to ensure that there's no warping or chemical reaction. Get the installation right and you'll have a beautiful marble countertop that will last for many years.
Don't Forget Travertine
Travertine is another extremely popular rock used as marble for countertops. This is also well worth discussing. Travertine is similar to compact limestone in that it's not a true marble but became crystallized while in a sedentary state. This also means that the crystals are a little smaller, although rarely as small as most versions of compact limestone.
In order to tell the difference between compact limestone and travertine, you have to be an experienced expert who knows what they're looking for. Travertine is inorganic because it is a chemical rock while compact limestone has an organic origin. It's found largely in Wyoming, New Mexico, and Nevada. There's also plenty of high-quality travertine in Italy.
Travertine is comprised largely of aragonite or calcite combined with limonite, which is also known as hydrated iron oxide. This composition is usually a result of rivers and waterfalls evaporating, leaving behind calcium carbonate. In particular, travertine emerges when spring water near a cave dries up.
The benefits of Marble for Countertops
There's a reason that marble is so popular in American kitchens. In fact, there are several reasons, including:
- Beauty: Few materials match the sheer beauty and elegance of a marble worktop.
- Hardness: Marble is incredibly hard and lacks the porousness and absorbability of other materials. This makes it easy to keep clean and ensures it lasts a really, really long time. Even granite, at least in geological terms, is not as hard as marble.
The Drawback of Marble for Countertops
There's one major problem with using marble for countertops: sensitivity to acids. Marble is a calcareous rock, meaning that it reacts to chemical substances. This becomes clear when you polish a marble, with the evidence of a harsh chemical reaction becoming obvious.
Any spill is likely to last a long time, leaving a ring or a splatter in the shape of the spillage. These may appear to be water stains, leading many kitchen owners to use sealants to try and stop any leakage. In truth, these are unlikely to be due to a leak but rather due to the chemicals that have spilled onto the top of the polished marble surface.
Penetrating sealers can work to prevent staining by stopping a foreign liquid from changing the color of the surface of the marble. However, they do nothing to prevent a chemical reaction which is usually the cause of these marks and dull spots. The acid will also damage any sealers you have used, rendering them all but useless.
Overall, polished marble, just like limestone, should not be used on kitchen countertops. At least, real marble shouldn't. Green marble - which is not a true marble - can be successfully used as kitchen worktops. That's because they have an entirely different chemical makeup that is resistant to acids and won't react badly.
If you're looking for a material for another area of the kitchen, where there's no constant heavy usage leading to wear and tear, then it's fine to use real marble. You'll have all the benefits of beauty and hardness, without worrying about acid corrosion. When cleaning these surfaces, use a gentle cleaner rather than any harsh chemicals. Try to find products designed specifically for marble that offer a more delicate clean.
Many people love the luxury of a marble floor but make sure you're aware of the required maintenance. You shouldn't use a polish but rather install a honed finish. Be prepared to slow down the effects of people walking on the floor regularly and potentially spilling harsh chemicals.
Marble for flooring is graded from A-D, with A being the most consistent and uniform and D being the least uniform, with many fragments that are not well-bonded together. Make sure you choose a grade A or B marble for your floor to ensure there are no cracks caused by people walking on the surface. Marble can also be used in bathrooms or other areas of the house.
Takeaway: learn the difference between true marble and what is sold as marble. Make sure you understand the material you're using and how to keep it properly maintained, wherever it's used in your home.