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Mohs Hardness: 7 
Specific Gravity: 2.65 
Reflective Index: 1.544-1.553 

Clear quartz crystals are made of silicon and oxygen, 
combined to form silicon dioxide. It is the most common 
single mineral in the earth's crust. It is found virtually
everywhere. It is found in "perfect" single crystals from 
microscopic size to many tons. Common sand is composed 
primarily of quartz.