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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/Transpar.aspx

A specimen with such characteristics is said to be transparent in thin splinters or sections. All minerals with a metallic luster are opaque. Most minerals with a ...

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.minerals.net/resource/Mineral_Value.aspx

For example, the mineral Rhodochrosite usually has a high value because its ... of undesirable coatings will also make a mineral more aesthetic and desirable.

www.gemsociety.org/article/what-is-a-gem

Even the most general definition of a gem has many exceptions. ... Most gems are minerals, but some, notably pearl and amber, are organics. ... If it makes your eyes light up, it's a true gem! ... specimens big and points in bulk, large malachite specimen hand size, faceted semi precious stones, certified Tanzanite, all for sale ...

www.gemrockauctions.com/learn/additional-gemstone-information/mineral-specimens

Apr 6, 2010 ... Mineral samples and crystals have been collected since our first ... Minerals composing oxygen make up almost half of the earth's crust.

www.nationalgeographic.com/science/earth/inside-the-earth/minerals-gems

A sapphire, the common name for the mineral corundum in its transparent blue form, sparkles. As seen here, some sapphires, when cut to a convex shape, ...