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en.wikipedia.org/wiki/Gemstone

A gemstone is a piece of mineral crystal which, in cut and polished form, is used to make .... For example, beryl, which is colorless in its pure mineral form, becomes emerald with chromium impurities. If manganese is added instead of chromium ...

www.gemrock.net/learn/gemstones

What Makes A Mineral A Gemstone? ... To qualify as a gem, the specimen should be hard and tough to resist scratching and have beautiful clarity, colour or 'fire'.

www.minerals.net/resource/property/Color.aspx

But there are many minerals which have slight additions of color-causing elements in some specimens that cause it to be a different color. For example, pure ...

www.minerals.net/resource/property/Streak.aspx

Information on the mineral property Streak. ... matter what color the actual mineral is. For example, Calcite occurs in many different colors, shapes, and varieties.

www.gemsociety.org/article/how-gems-are-classified

For example, all minerals that contain silica are ... Identifying the class of the gem makes it ...

www.gemselect.com/other-info/minerals-rocks-gems.php

Dec 21, 2007 ... What is the difference between a mineral, a rock and a gemstone? ... of a gemstone is not particularly scientific since it does not make much ...

geologycafe.com/gems/chapter2.html

The structure of minerals and their bonding make a lot of the difference in the minerals' properties, for example hardness. These factors, particularly the ...

geologycafe.com/gems/labs/lab1.html

Example of minerals with metallic luster include pyrite and galena. Another ... Labradorite makes an attractive building material and semiprecious stone. Schiller ...

www.smithsonianeducation.org/educators/lesson_plans/minerals/minerals_crystals.html

Born of fluid, heat, and pressure, minerals dazzle us with their breathtaking ... that have been at work for billions of years continue to make more minerals. ... students may find a single mineral specimen such as marble, which is pure calcite.