Amethyst

• The variety of the mineral quartz; hexagonal (trigonal) crystal system; chemical composition SiO2 
• transparent; material used for beads and carvings may be translucent 
• bluish purple to purple to reddish purple; often shows a slight shift in hue under different lighting
  

Trade Names:

• Uralian or Siberian amethyst – deep reddish purple to purple-red
• ametrine – bi-colored variety with amethyst and citrine colors

Identification:

• Optic Character: DR, uniaxial positive 
• Refractive Index: 1.544-1.553 (very constant) 
• Birefringence: .009 
• Dispersion: .013 
• Pleochroism: weak to moderate purple and reddish purple 
• Ultraviolet Fluorescence: usually inert; may show weak blue (SW) 
• Cause of Color: color centers involving iron impurities and irradiation 
• Specific Gravity: 2.66 (+.03, -.02)
• Polish Luster: vitreous 
• Fracture: conchoidal
• Luster: vitreous
• Cleavage: none 
• Identifying Characteristics: color zoning, twinning, liquid, 2-phase, and 3-phase
• inclusions, negative crystals, may show bull’s-eye or Airy’s spiral optic figure 
• Hardness: 7 
• Toughness: good

Enhancements:

• Method: heat treatment

Effect: lightens the color of very dark amethyst; removes smoky component of color; produces citrine and green quartz
Prevalence: occasional
Detection: undetectable
Stability: excellent

Birthstone Designation(s):

Amethyst – February, Pisces (approximately Feb. 19 – Mar. 20), 8:00 am, Wednesday, 6th wedding anniversary 

Major Sources: Brazil, Uruguay, Namibia.

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