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
