Hobbies and Crafts Reference Center Home http://web.ebscohost.com/hcrc/delivery?vid=3&hid=106&sid=2800393d...

Record: 1 DUMORTIERITE. Peterson Field Guide to Rocks & Minerals, 1996, p362-363, 1p Abstract: The article presents information on the subsilicate mineral dumortierite. It is rarely in small embedded distinct crystals, usually in very finely fibrous compact masses. In the U.S., dumortierite is most common in the West and has been mined in Oreana, Nevada, for spark plug ceramics. The blue is found in Los Angeles County, California, with a gray quartz, and has been carved as an imitation lapis lazuli in China. New York City building excavations produce fair dumortierite needles. The dumortierite found in Alpine, San Diego County, California, has a purple fluorescence.; (AN 18280411) Database: Hobbies & Crafts Reference Center Section: PART II MINERAL DESCRIPTIONS DUMORTIERITE

Al8BSi3O19(OH) Pl. 64

Orthorhombic -- Rhombic bipyramidal 2/m 2/m 2/m

Environment: Scattered single crystals in pegmatites, in quartz concentrations in metamorphic rocks, and in gneisses and schists; also in solid, economically minable crystal masses. Crystal description: Rarely in small embedded distinct crystals; usually in very finely fibrous compact masses. Physical properties: Violet, pink-violet, or blue. Luster glassy to pearly hardness 7; specific gravity 3.3-3.4 (but usually impure); fracture conchoidal; cleavage poor pinacoidal. Translucent to transparent gemmy (very rare). Composition: Alkaline aluminum borosilicate (64.6% Al2O3, 55% B2O3, 28.5% SiO2, 14% H2O). Tests: On the charcoal under the blowpipe, it whitens, but with cooling, the color partially (or entirely) returns. Sometimes fluorescent blue after firing, sometimes naturally purple fluorescent.

Distinguishing characteristics: Bright color and fibrous appearance are distinctive, and distinguish it from nonfibrous-looking lazulite and lazurite (which usually have yellow to orange fluorescent associates). The great hardness distinguishes the purple variety from similar-appearing rare species or lepidolite.

Occurrence: In the U.S., dumortierite is most common in the West and has been mined in Oreana, Nevada, for spark plug ceramics. The blue is found in Los Angeles Co., California, with a gray quartz, and has been carved as an imitation lapis lazuli in China. Scattered needles through quartz are found in many localities and are recognized by their color. New York City building excavations produce fair dumortierite needles. Alpine, San Diego Co., California, dumortierite has a purple fluorescence. Blue "knots" in white quartz occur near Karibib, Namibia. A light "blue quartz" quartzite (comparable to green mica-saturated aventurine) from Brazil is colored by dumortierite. Several carat-sized gemstones, strongly dichroic in blue and white, have been found as waterworn Brazilian pebbles.

Peterson Field Guides to Rocks and Minerals by Frederick H. Pough. Text and illustrations Copyright © 1953, 1955, 1960, 1976, 1996 and © renewed 1981, 1983, 1988 by Frederick H. Pough. Published by Houghton Mifflin Company. Peterson Field Guides and Peterson Field Guides Series are registered trademarks of Houghton Mifflin Company. All rights reserved.

1 of 1 6/17/2010 2:46 PM