Page 15 - June SRG

Slippery rock Gazette
White Granite, White Quartzite, and White Marble
Continued from page 14
The fact that these two stones look alike is why they are so fre- quently mislabeled and misunder- stood. Your best bet is to rely on the way the stones behave rather than how they look. Thankfully, marble and quartzite have consis- tent traits that you can use to tell them apart.
• Quartzite is much hard- er than marble and slightly harder than granite.
You can use a glass tile or a knife blade to gauge the hard- ness of a stone. Quartzite will leave a definite scratch on glass, and a knife blade will not eas- ily scratch the stone (though it may leave a silvery mark on the stone, which is the metal rubbing off on the stone). See also A Deep Dive Into the Properties of Quartzite, slipperyrockgazette .net/archives for more on quartzite.
• Marble is relatively soft.
A knife blade will make ob- vious scratch marks on marble; and marble will not scratch glass. Some marbles, like Super White or Fantasy Brown, may have iso- lated pockets of quartz amid an overall composition of marble. When in doubt, check a few dif- ferent areas of the stone.
• Quartzite is not affected by common acids.
Vinegar, lemon, wine, citrus, or any other common acid won’t affect quartzite. Strong chemicals like oven cleaner or rust remover can damage almost any stone, though, so be careful with those.
• Marble is acid-sensitive.
The mineral calcite is dissolved
by acids, and many types of stone contain calcite, such as limestone, onyx, travertine, and marble. (Science trivia: this is why acid rain caused damage to buildings and monuments before we got a handle on the pollution that causes acid rain.) Dolomite is a mineral that is chemically similar to calcite, and it’s also affected by acids but not as quickly. In either case, acids leave an etch mark or a dull spot on the surface of the
stone. Etches do not affect the structural integrity of a stone, and they can be polished out if need be. For people who love marble, etches are often considered a part of the living surface of the stone, which develops depth and charac- ter over time. If that idea makes you cringe, then you know marble is not for you. Choose quartzite or granite instead!
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By contrast, marble and quartzite both have a smaller grain size and all the grains in the white areas are the same color. This is Lincoln marble.
Below: Most marbles and quartzites are fine grained, but a few have larger crystals, such as this slab of Allure quartzite. Note how all the crystals are the same color, which is not the
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Above and Center: Super White and Calacatta Gold are examples of marble breccia. The stone was fractured into pieces and then the fractures were filled in with minerals to create a strong, solid rock. Both the fracturing and the re-cementing happened deep under- ground, under tremendous pressure. The chunks of marble make the rock look coarse-grained, like granite. But it’s actually frag- ments of fine-grained stone. It can be hard to tell the difference.
case with white granites.