Obsidian

 Mohs scale
  5.0 - 5.5
 Specific Gravity
  2.35 - 2.60
 Refractive Index
  1.450 - 1.550
 Crystal system
  Amorphous
 Chemical Composition
  SiO2

 Sign of Zodiac (Click on the constellation for more information)
 Chakra (Click on the chakra for more information)
 Birthstones (Click on the month for more information)
 
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