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Tanzanite’s Interesting Color
The mineral zoisite naturally occurs in a wide range of colors that include colorless, gray, yellow, brown, pink, green, blue, and violet. The name “tanzanite” is used for a color variety of zoisite that ranges from blue, through violet, to violetish purple. This type of color-variety name is not unusual. The name “ruby” is used…
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A Modern Gem and Birthstone
Although nearly all of the world’s most popular gemstones have been known and used for hundreds of years, tanzanite was not discovered in commercial quantities until the 1960s. In the short time since then, it has become the second most popular blue gem after sapphire. It is one of a very small number of gems of any color that have been discovered…
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What is Tanzanite?
Tanzanite is a trade name that was first used by Tiffany and Company for gem-quality specimens of a mineral named zoisite with a blue color. Tiffany could have sold the material under the mineralogical name of “blue zoisite,” but they thought the name “tanzanite” would stimulate customer interest and be easier to market. The name “tanzanite” was given because…
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Other Uses of Corundum
Corundum has many other uses. It is chemically inert and resistant to heat. These properties make it a perfect material for making refractory products such as fire brick, kiln liners, and kiln furniture. Today, these products are usually made with synthetic corundum. Pure corundum is colorless, transparent, durable, and scratch resistant. Large crystals of clear…
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Ruby Lasers
Synthetic corundum is an essential part of many lasers. In fact, the first working laser was a “ruby laser,” made by Theodore Maiman at Hughes Research Labs in 1960. It employed a synthetic ruby crystal as the “gain medium.” The gain medium is a material in the laser that is the target of an intense…
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“Jewels” and “Crystals” in Watches
In the mid-1800s, watch makers in Switzerland needed tiny bearings that were highly resistant to abrasion. They discovered that they could drill a hole into a tiny piece of corundum and use it for a smooth-running, long-life bearing. The corundum was much harder than the metals used to make the moving parts of a watch,…
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Use as a Gemstone
In the gemstone and jewelry market, almost all of the attention goes to a small group of gems known as “the big four”: diamond, ruby, sapphire, and emerald. Two of these, ruby and sapphire, are gem corundums. These most popular gems are highly sought after and have been mined in many parts of the world for thousands of years. Today, millions…
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Emery
Emery stone is a granular metamorphic or igneous rock that is rich in corundum. It is a mixture of oxide minerals, typically corundum, magnetite, spinel and/or hematite. It is the most common form of natural corundum that has been used to manufacture abrasives. The use of emery as an abrasive has declined significantly in the last several decades. It…
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Hardness and Use as an Abrasive
The extreme hardness of corundum makes it especially useful as an abrasive. Crushed corundum is processed to remove impurities and then screened to produce uniformly sized granules and powders. These are used for grinding media, polishing compounds, sand papers, grinding wheels, and other cutting applications. Some problems with using natural corundum as an abrasive are…
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Geologic Occurrence of Corundum
Corundum is found as a primary mineral in igneous rocks such as syenite, nepheline syenite, and pegmatite. Some of the world’s most important ruby and sapphire deposits are found where the gems have weathered from basalt flows and are now found in the downslope soils and sediments. Corundum is also found in metamorphic rocks in locations where aluminous shales or bauxites have…