Sard

Red-brown to brown variety of Chalcedony (named after town in Asia Minor). No strict separation from carnelian (darker and browner stones are usually called sard), with common deposits and uses.
General Information
A variety or type of:Chalcedony, which is a variety of Quartz
Chemical Formula
SiO
 
2
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
Photos of natural/un-cut material from mindat.org
Sard Treatments
The color may be lightened by heat-treatment - Blue Chart Gem Identification, Herve Nicolas Lazzarelli, 2010, p 7
Physical Properties of Sard
Mohs Hardness6.5 to 7
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Specific Gravity2.58 to 2.63
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
Cleavage QualityNone
Walter Schumann, Gemstones of the world (2001)
FractureConchoidal
Arthur Thomas, Gemstones (2009)
Optical Properties of Sard
Refractive Index1.535 to 1.539
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)
PleochroismAbsent
Walter Schumann, Gemstones of the world (2001)
DispersionNone
Walter Schumann, Gemstones of the world (2001)
Colour
Colour (General)Brown
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
More from other references
TransparencyTranslucent,Opaque
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
LustreWaxy,Resinous
Arthur Thomas, Gemstones (2009)
Crystallography of Sard
Crystal SystemTrigonal
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
HabitFibrous to grained aggregate
Ulrich Henn and Claudio C. Milisenda, Gemmological Tables (2004)
Further Information
Mineral information:Sard information at mindat.org
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