Crystal

• Quartz species; hexagonal (trigonal) crystal system; chemical composition SiO2 
• rock crystal – transparent colorless 

Identification:

• Optic Character: DR uniaxial positive or AGG (depending on variety) 
• Refractive Index: 1.544-1.553 (very constant) 
• Birefringence: .009 (may not be detectable in aggregate varieties) Dispersion: .013
  Pleochroism: none 
• Specific Gravity: 2.66 (+.03.-.02) 
• Polish Luster: vitreous Fracture: conchoidal to uneven or granular (in aggregates)
  Luster: vitreous 
• Cleavage: none 
• Identifying Characteristics: 2-phase, and 3-phase lusions, negative crystals, may show bull’s-eye or Airy’s spiral optic figure. 
• Hardness: 7 
• Toughness: good.

Birthstone Designation(s):

rock crystal – Monday

Major Source: Brazil, Madagascar, US, Alps.

Stone information is reference from

Gem Reference Guide, Published by GIA. ISBN 0-87311-019-6

Gemstones of the World, Published by Sterling Publishing Co., Inc NY, ISBN 1-4027-4016-6

Encyclopedia of GEMSTONE, Published by ISHINSHA CO., LTD. ISBN 978-986-251-831-1