Marble Properties: A Geological Look at Classic Marble

In this paper we will look at marble properties from a geological point of view. Believe it or not, some people wouldn’t dream of designing a kitchen without marble. Others decry that choice, citing marble’s imperfections and fragility. Many are caught somewhere in the middle. They are in love with marble’s irresistible appeal, but uncertain if it’s the right choice for their circumstance. In an attempt to create the perfect material, legions of synthetic products claim to look just like marble. But marble enthusiasts aren’t swayed. Few stones can match the warm glow, the softly flowing colors, the timelessness, and the authenticity of marble. There’s good reason this stone has been used for over 5,000 years.

Marble as a Metamorphic Rock

Marble is a metamorphic rock. It once was a different kind of rock. Then, it was transformed by a change of circumstance. Before marble becomes marble, it is first limestone. The limestone forms on the shores and floors of tropical seas.

From Limestone to Marble

Limestone is an accumulation of shells, shelly fragments, microscopically tiny shells, and dissolved shells. Depending on the conditions at a particular beach or sea, limestone’s shelly sediment may be punctuated with occasional layers of clay or lenses of sand. But by and large, limestone is an assortment of shell-remnants, which are made of the mineral calcite.

Marble Formation through Heat

When a limestone seabed gets dragged down into the Earth’s crust, the additional heat transforms the calcite grains and fuses them together tightly. The dynamic action of rock layers as they become buried, twisted, and shoved around causes the original flat-lying layers to bend, buckle, and swirl together. A rock in this heated state doesn’t melt. It’s simply warm and flexible, much like a chocolate bar left in your pocket. This process of heating and warping is responsible for marble’s trademark aesthetic of gracefully flowing bands of color. The grey swirls in marble are simply clay layers that got folded, smeared, and re-folded into the marble like a ribbon of chocolate infused throughout fudge ripple ice cream.

Marble Colors and Textures

Part of what makes natural stone so appealing is the huge range of colors and variations expressed in solid rock. On one hand, these patterns tug on our heartstrings and offer aesthetic possibilities. On the other hand, each of these variations has its root in some sort of geologic process. Most marble is white. The classic, white marble is pure calcite, without intervening minerals to lend it color. Marble can take on a delightful range of hues and textures. Pink marble is tinted by iron oxide, as is golden marble. Green marble and deep red marble contain serpentine, rich in magnesium. Fossil-rich limestone becomes graphite-infused marble, as the carbon in fish, algae, or seaweed reverts back to the elemental carbon in graphite when the rock is heated.

Marble Properties

The mineral content of marble is the same as the limestone it came from, and both of these stones are made of calcite, AKA calcium carbonate, AKA CaCO₃. Calcite is one of the more common minerals on Earth’s surface; in addition to limestone and marble, calcite is the primary ingredient in travertine and onyx.

Marble Hardness

Calcite has a few properties that you should know about before you fall head over heels in love with a stunning marble slab. Calcite is 3 on Mohs hardness scale, which means it will get scratched by knife blades, ceramics, and a cast iron skillet accidentally slid across the kitchen island.

Marble Strength

Calcite is also chemically reactive with common acids, such as those found in lemonade, wine, and colas. When acidic liquids land on a marble slab, a tiny amount of the stone is dissolved, or etched. This doesn’t affect the integrity of the stone, but it does leave a slight change in the color and or luster of the stone. On a polished stone, an etch looks like an unpolished area. Etches can be polished out, or they can be left alone and considered part of the natural patina that marble will acquire over time.

Marble Acid Neutralization

Marble is ground up into antacid tablets because calcite neutralizes acid, which makes your stomach feel better. That also explains why acid makes a mark on marble. The marble reacts with the acid, neutralizing the acid, but damaging your countertop in the meantime. Ironically, when your teenager dribbles pickle juice on a brand new countertop, you may find yourself reaching for the antacid, triggering the same chemical reaction both on the countertop and in your digestive tract.

Marble Star Cracks

The last piece of potentially bad news is that marble can form star cracks or stun marks if a heavy, hard object falls on it. Star cracks look like small, light-colored areas where the impact occurred. This is usually an aesthetic issue, not a structural one, but if an impact occurs at the edge of the stone, it can chip or flake.

Marble Staining

A common misconception is that marble stains easily. However, this is actually quite rare. The metamorphism that bakes the stone also knits the minerals together tightly. Porosity for marble is similar for that of granite. Marbles are typically sealed to reduce the likelihood of staining.

Now you can see why some people love marble while others think that marble-lovers are crazy. To some, the nicks and etches on a marble surface add character and mark the passage of time in a busy household. To others, each blemish resonates as a personal loss. Marble isn’t for everybody. It can be difficult to maintain, especially in high traffic areas. After all, nothing matches the beauty of natural marble.

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Sources

usenaturalstone.org/mad-marble-geological-look-classic-stone/

www.houzz.com/discussions/3059285/brand-new-marble-countertops-have-pitting