Page 30 - Demo

Above: This is not natural stone – it’s a slab of engineered quartz. One of the clues to identifying manmade quartz, and the reason why we say it does not look “natural” is because the “crystals” are all blob-shaped and have the same luster as the rest of the surface. The recognizable rectan- gles of feldspar and the glassiness of real quartz are absent.
Calcite fills in pore spaces in this limestone. On the edge of this slab is a small, crystal-lined pocket.
Calcite crystals reflect light off of their flat planes. Leathered Fantasy Brown.
Calcite can look similar to quartz because it’s translucent, but quartz is glassy while calcite has a softer, satiny luster. But a quick hardness test will sort it out definitively. Below: a spectacular slab of onyx.
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30|January 2020
Know Your Minerals – Part 3
Dolomite
This is calcite’s cousin, and shares similar color and properties of calcite with a few exceptions. Compared to calcite, dolomite is slightly less susceptible to etching from acids, giving you some time to wipe up spills before the stone is affected.
Identifying features:
•Dolomite and calcite look alike and you can’t tell them apart visually.
•The test for dolomite is called the ‘powdered rock acid test.’ Calcite will have a fizzing reac- tion when in contact with diluted hydrochloric acid. Dolomite will not, unless the stone is powdered first. To do this test, use a nail
or tip of a knife and scratch up an area of the stone. Leave the stone dust in place, and then put one drop of acid on it. If the stone is dolomite, it will have a weak, bubbling reaction. If it’s some other type of mineral altogether, like feldspar, there will be no re- action at all.
Properties:
Dolomite has a Mohs hardness of 3.5, which is slightly harder than calcite. Dolomite also etches more slowly than calcite, but it will still etch.
Example: Super White is a well known dolomitic marble that is frequently mislabeled as quartzite.
Slippery rock Gazette
Superpower: Proximity to dolomite strengthens teeth and makes dental visits less stressful.
Now, let’s see what you’ve learned. Turn to page 23 for a short test of your mineral saavy. Answers are below .
Karin Kirk is a geologist and science educator with over 20 years of experience and brings a different perspective to the stone industry. Karin is a regular con- tributor to usenaturalstone.com and the Slippery Rock Gazette. Contact her at karinkirk@ gmail.com .
Continued from page 18
Properties:
The best way to tell calcite from quartz or feldspar is by its prop- erties. Calcite has a Mohs hard- ness of 3, which is harder than a fingernail but softer than glass. A sharp-tipped nail or pocketknife will leave a definitive scratch in calcite. Also, vinegar dripped onto calcite will often gently fizz.
These same properties apply to
slabs and tiles. Stones made of calcite can be etched from acids, and can also be scratched by metal or ceramic kitchen implements.
Examples:
All marbles and limestones are made of calcite. Some well-loved examples are Carrara, Danby, White Cherokee, and Colorado White marbles; or Belgian Blue, Fossil Black, Saint Pierre, or Emperador limestones.
Superpower: Calcite makes it easier to keep world events in perspective and has been shown to reduce social media use.
© MARK ANDERSON. www.andertoons.com
Mineral Quiz, Page 23 A: Quartz B: Feldspar C: Garnet D: Amphibole