Countertop Geology: Marble and quartzite and granite, oh my!
This is round three of the Great Rocks Thread! It appears we at GW have a large appetite for discussing and sharing pictures of rocks.
Please post your rock questions here. I've copied the first post from Rocks 102 here to lay the foundation.
Quartzite and marble are hopelessly (deliberately?) mixed up in the decorative stone industry. My point, aside from just loving rocks, is to help folks learn how to tell the difference between the two so you are not at the mercy of a sales rep when a multi-thousand dollar purchase hangs in the balance.
Quartzite is much harder than marble and will not etch when exposed to acids. You can tell the difference between quartzite and marble by doing the scratch test.
Take a glass bottle or a glass tile with you when you go stone shopping. (Glass tile idea is courtesy of MaggiePie11, what a good idea!) Find a rough, sharp edge of the stone. Drag the glass over the edge of the stone. Press pretty hard. Try to scratch the glass with the stone.
Quartzite will bite right into the glass and will leave a big scratch mark.
Any feldspar will do the same. (Granites are made mostly of feldspar)
Calcite and dolomite (that's what marble and limestone are made of) will not scratch. In fact you will be able to feel in your hand that the rock won't bite into the glass. It feels slippery, no matter how hard you press.
PS - don't press so hard that you risk breaking the glass in your hand. You shouldn't need to press that hard!
For reference, here are links to the other rock threads, in which many types of rocks have been discussed. If you read through both of these threads you will earn an honorary degree in Kitchen Geology.
With that, let the rock conversations continue!