dumortierite (thing)

Chemical Composition:Al₇(O₃(BO₃)(SiO₄)₃)
Mohs' Hardness: 7-8.5
Specific Gravity: 3.26-3.45
Cleavage: Perfect
Transparency: Opaque
Refrative Index: 1.686-1.723
Double Refraction: -0.037
Dispersion: None

Dumortierite was first described in 1881 by M.F. Gonnard, who named it after French Paleontologist Eugene Dumortier. Dumortierite is usually found in a denim-blue color but can vary from a blueish-lavender to a very dark, almost black, blue. Because of its coloration, Dumortierite is often confused with sodalite, lazurite and lazulite. However, sodalite will always have more white portions, due to the presence of calcite in the stone. Both lazurite and lazulite are not fibrous stones, whereas Dumortierite is fibrous. This case of mistaken identity is not always a bad thing. In China, dumortierite is sometimes used as a replacement for the more expensive lapis lazuli, and used for trim around furniture among other uses.

Dumortierite is not the best stone for jewelry as, at best, its lustre is vitreous, and not brilliant, like a diamond, or shiny, like gold. It is also a very opaque stone, which does not allow the stone to be cut as finely as a diamond, ruby, sapphire or other such stone, as the facets will not be seen. However, dumortierite has been formed into earrings and necklaces. The bangles are pushed as jewelry that goes well with blue jeans, as the colors are complementary.

Dumortierite is usually found in metamorphic rocks which are rich in aluminum. Veins of dumortierite have been found in Lyons, France, the Malagasay Republic, Italy, Namibia, Sri Lanka, Germany, Poland, Canada, Brazil, Nevada, California and Arizona. The dumortierite found in Brazil is actually dumortierite quartz. Dumortierite quartz consists of dumortierite crystals growing in a matrix of quartz, creating a beautiful light blue color. Dumortierite grows in an orthorhombic crystalline structure, usually as columns of crystals.

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Sources:
Precious Stones, by Dr. Max Bauer. Charles E. Tuttle Company: Rutland Vermont and Tokyo, Japan, 1969
Gemstones of the World, by Walter Schumann. Sterling Publishing Co., New York, 1979
Simon and Schuster's guide to Rocks and Minerals, Simon and Schuster Inc. New York, 1978
http://www.mineralgallery.co.za/dumortierite.htm
http://78.1911encyclopedia.org/D/DU/DUMORTIERITE.htm