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(September 2008)| Unprocessed sample of ammolite, a "dragon
skin" pattern is apparent |Category||fossilized, mineralized
Ammonite shell| |CaCO3 aragonite polymorph, with minor amounts
of calcite, pyrite, silica, and other impurities| |Color||Gray
to brown, with primarily red to green iridescence.|
|Cleavage||no true cleavage| |Fracture||uneven to granular|
|Mohs scale hardness||4.5 - 5.5| |Luster||greasy to dull|
|Specific gravity||usually about 2.70 (varies with mineral
content)| |Optical properties||anomalous aggregate reaction|
|Refractive index||usually 1.52 - 1.68 (varies with mineral
content)| |Birefringence||usually 1.55 (varies with mineral
content)| Ammolite, a semi-precious opal-like organic gemstone
found primarily along the eastern slopes of the Rocky Mountains
of North America. It is made of the fossilized shells of
ammonites, which in turn are composed primarily of aragonite