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Mohs Hardness: 7 
Specific Gravity: 2.65 
Reflective Index: 1.544-1.553 
  
Smoky quartz is a macrocrystalline variety of the mineral 
Quartz (SiO2). Quartz is the most abundant single mineral on
earth. It makes up about 12% of the earth's crust, occurring
in a wide variety of igneous, metamorphic and sedimentary 
rocks. 
 Quartz varieties are commonly separated into two groups
based on the size of the individual grains or crystals; 
macrocrystalline quartz in which individual crystals are 
distinguishable with the naked eye, and cryptocrystalline 
quartz in which the individual crystals are too small to be 
easily distinguishable under the light microscope.