Dallasite

A volcanic breccia, it contains well-defined, thin, rectangular chunks of green or brown lava set in a silicifed matrix, can be classed as a type of jasper.

Named for Dallas Road, Victoria, British Columbia, Canada, which runs along the southern tip of the city where it was found.
General Information
A variety or type of:Jasper, which is a variety of Chalcedony, which is a variety of Quartz
Physical Properties of Dallasite
Mohs Hardness6.5 to 7
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Specific Gravity2.58 to 2.91
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Optical Properties of Dallasite
Refractive Index1.540 (+/-)
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Optical CharacterUniaxial/+
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
Birefringence0.008 to 0.010
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
Colour
Colour (General)Green, black
Gemdat.org, Management Team (2012)
Crystallography of Dallasite
Crystal SystemTrigonal
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
Further Information
Mineral information:Dallasite information at mindat.org
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