December 12, 2013

Geology in your Kitchen: The Mystery of Super White

by Karin Kirk

Any geologist will tell you, “geology is all around us.” One unlikely place that this is especially true is on your kitchen countertop. Once strictly the domain of luxury kitchens, natural stone countertops are becoming more common in homes at many price points across the US.

Super White countertop.



Demand for granite countertops has risen by over 400% since 1997 and Forbes magazine estimates that Americans have collectively spent over $12 billion on stone countertops since the 1990s. These rocks bear fanciful names such as Azul Platino, Jet Mist, and White Leopard and are available in colors and patterns to suit just about any taste.

But what are these rocks? (You won’t find White Leopard or Jet Mist in any geology texts.) And why should we care?

A slab of super white sold as granite.



Decorative stone is often classified into two neat categories: granite and marble. Nearly all rock types are lumped into these catch-all groups, which is not only incorrect but is also bound to create confusion. On one hand, maybe it doesn’t matter if your kitchen countertop goes by the name of quartz syenite or Café Bahia. As long as aesthetic suits your taste, perhaps the particular mineral contents or textural elements are unimportant.

Maybe – until you ponder the rigors of a busy kitchen. Sharp objects, acidic liquids, abrasive cleaners and lots of daily wear and tear can do some serious damage to a countertop, so a stone in this environment had better be up to the task.  The ideal work surface is harder than the objects around it so that it doesn’t get scratched, strong enough to withstand the occasional impact from a cast iron skillet, and resistant to acids like lemon juice and vinegar.

This is a tall order and not every rock sold for a countertop is well-suited for it.

A case in point is a popular rock sold under the name “Super White.” It’s a kitchen designer’s dream, with soft, flowy veining and a gorgeous grey-white color that is in high demand. It is said to “look like marble but wear like granite.” Depending on where you shop, it can be labeled as either granite, quartzite or marble. To a geologist these sound like a potential misconceptions.

But, even a misunderstood rock can be demystified by employing some basic rock identification techniques.  The key elements for kitchen suitability are a rock’s hardness and resistance to being dissolved by household acids. These are straightforward to suss out with a sample of Super White.

Hardness can be determined by seeing if the rock scratches glass. Granite will scratch glass easily but no matter how hard you press, marble simply cannot put a dent into glass. When put to the test, Super White does not scratch glass. Strike one against the hyperbole of “wearing like granite.”

Resistance to acids is problematic for countertop rocks, particularly marble. The telltale “etch” on a kitchen counter is a result of the surface of the rock dissolving from contact with acid. Kitchens abound with acidic liquids such as citrus, wine, pickle juice and tomato sauce. While marble is a beautiful choice for kitchen aesthetics, it is damaged by acids, thus offering a love-hate dilemma for kitchen designers. Hence the allure of a rock like Super White that indeed looks like marble but is said to behave like granite.

Well, the Super White sample failed to stand up to the acid test. Geologists use diluted hydrochloric acid to identify the mineral calcite, which is the primary ingredient in marble. A single drop of acid on calcite will yield faint bubbles as the mineral dissolves and gives off carbon dioxide gas. Alas, when acid is put on Super White it does not bubble at first. But, if the surface of the rock is scratched up, then the bubbles appear. This is the classic test for dolomite, which is a close cousin to calcite. Dolomite is slightly more resistant to acid than calcite, but it will still dissolve over time.

Taking all of the rock’s characteristics into consideration, Super White would properly be called dolomitic marble.  Even to a geologist, dolomitic marble does not exactly roll off your tongue. Super White certainly is a more palatable and marketable name. Is Super White a suitable rock for your countertop? It depends on your tolerance for etching and scratching. But the important thing is to know what you are buying, which is why some geologic skills are handy here.

But after all the geologic diagnoses, a caveat remains. Not all Super Whites are dolomitic marble. Some are likely to be calcitic marble, and others may be quartzite, which would indeed wear like granite. All are confusingly lumped under the same name. So if you go to buy stone countertops, bring along a glass tile and see if the rock can scratch it. Or better yet, just bring along a geologist, and be prepared for a very enthusiastic journey through the slab yard, a veritable candy store for those among us who have an endless appetite for rocks.

 

For more information

To learn more about describing and defining minerals, read Visionlearning’s Defining Minerals and Properties of Minerals modules in our Earth Science: Rocks and Minerals series.

Latest trends in the U.S. Stone Industry

Granite Countertop Craze Has Cost U.S. More Than First Gulf War  (Forbes)

The Lowdown on Super White (Kitchens Forum discussion of this topic)

Karin Kirk

Written by

Karin Kirk is a freelance writer and educational curriculum developer. She holds Bachelor’s and Master’s degrees in geology and has taught undergraduate geology, environmental science and climate change in both face-to-face and online courses. Prior to joining the Visionlearning team, she worked for the Science Education Resource Center at Carleton College where she was part of several educational projects focused on improving undergraduate science education. In the winter months, she continues her passion for education in her role as a ski instructor at Montana’s rugged Bridger Bowl ski area.