Ammolite

Ammolite is an 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... Wikipedia

• Category:  fossilized, mineralized Ammonite shell
• Formula, (repeating unit):  Ca C O 3 aragonite polymorph, with minor amounts of calcite, pyrite, silica, and other impurities
• Color:  Gray to brown, can be radiant blue, with primarily red to green iridescence.
• Cleavage:  no true cleavage
• Fracture:  uneven to granular
• Mohs scale hardness:  3.5 - 4.5
• Luster:  greasy to dull
• Specific gravity:  usually about 2.70 (varies with mineral content)
• Polish luster:  vitreous
• Optical properties:  anomalous aggregate reaction
• Refractive index:  usually 1.52 - 1.68 (varies with mineral content)
• Birefringence:  0.135 - 0.145
• Pleochroism:  none
• Ultraviolet fluorescence:  variable
• Data source:  DuckDuckGo