Silicates: dumortierite
Diagnostic Card.
Al 7 O 3 BO 3 (SiO 4)3
Crystal system orthorhombic
8.5 Hardness
Specific gravity 3.4
Cleavage clear
fracture brittle
Color sky blue
Gloss silky glass
Named in honor of French paleontologist A. Dumortier. It is found in Brazil, Sri Lanka, Canada, Madagascar, Namibia, the United States, France (near Lyon), Poland. Dumortierite be confused with azurite, lapis lazuli, sodalite. There are close coalescence of dense mineral quartz.
In nature, there is a fiber-ray units intense sky-blue, greenish-blue, purple and bright red color. Gloss silky glass. Intense blue, blue - gray with brownish tinge, rarely red.
Chemical composition. Calcium Oxide (CaO) 0.68%, boron oxide (B2O3), 5.54%, alumina (Al2O3) 59.75% Iron Oxide (Fe2O3) 2.48% titanium oxide (TiO2) 0,95%, dioxide kremyaiya (SiO2) 28,51%, water (H2O) 2.12%. Class symmetry. Rombo - bipyramidal - mmm. Aggregates. Fibrous, radiant.
Diagnostic features.
Do not melted in the flame of a candle, and not amenable to the action of acids.
Origin.
It occurs as an accessory mineral in gneiss, granulites, pegmatites and contact-metamorphic rocks.
Place of Birth.
Installed near Lyon (France), in Volfshau in Silesia, near Rio de Janeiro (Brazil), to Nacozari (Mexico), in Ambatalahinanahari (Madagascar). In the states of Nevada, Arizona and California (USA) dumortierite developing an industrial scale (used in the manufacture of ceramics).
Dumortierite. Namibia. Photo: © AA Evseev.
Dumortierite. N`Rougas Suid farm, Kernhardt, Sev. Cape Prov., South Africa. Photo: © AA Evseev.
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