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Roger Weller, geology instructor                                         

wellerr@cochise.edu
Quartz Family Gemstones-by Audrey LaClair
                            
                                   Amethyst
 

The name amethyst is derived from the Greek term "not drunken".  Amethyst is a popular gemstone and is a form of quartz, in fact the most valued member.  It is February's birthstone.  It is said that amethyst would be much more expensive if not for it's large availability.  You can find amethyst at a widespread number of locations, but not all are the same.  Each region, even some single mines, can create unique amethysts.  And thus geologists can often times locate an amethyst back to it's original mine.

photo by R.Weller

"Amethyst can occur as long prismatic crystals that have a six sided pyramid at either end or can form as druzes that are crystalline crusts that only show the pointed terminations. As a mineral specimen, amethyst is popular for its color and nice crystal shapes that produce a handsome, purple, sparkling cluster" (http://mineral.galleries.com/minerals/gemstone/amethyst/amethyst.htm)

photo by R.Weller

"The purple color of amethyst is due to small amounts (approximately 40 parts per million) of iron (Fe⁴⁺) impurities at specific sites in the crystal structure of quartz. The difference between amethyst and citrine is only the oxidation state of the iron impurities present in the quartz. Upon heating, the iron impurities are reduced and amethyst's purple color fades and becomes yellow to reddish-orange (citrine), green, or colorless depending on the site and original oxidation state of the iron impurities present and the amount and duration of the heating. The amethystine color usually can be regained by irradiation which re-oxidizes the iron impurities" (http://www.mineralminers.com/html/ameminfo.htm). 

In history, amethyst has been used against drunkenness and overcoming addictions.  It has also been used for insomnia, headaches and hearing disorders.  Some sources say it can be used to stabilize mental disorders.  Amethyst is worn to make the wearer gentle.  Some of it's powers are love, healing, courage, happiness, dreams, and peace.

PHYSICAL PROPERTIES

·        Amethyst Chemical composition: SiO₂ (minor Fe⁴⁺ impurities cause amethyst's color)

·        Class: tectosilicate

·        Crystal system: Hexagonal-R; 32 (trigonal-trapezohedral)

·        Crystal habit: Macroscopic crystals occur as horizontally striated hexagonal prisms terminated by a combination of positive and negative rhombohedrons forming six sided pyramids. Amethyst often occurs as drusy masses showing only the rhobohedral terminations. It can also be massive.

·        Twinning: Dauphine twin with c the twin axis, Brazil twin with {1120} the twin plane

·        Specific gravity: 2.65

·        Index of refraction: 1.54-1.55

·        Birefringence: 0.009

·        Pleochroism: distinct

·        Hardness: 7

·        Color: light to dark purple

·        Luster: vitreous

·        Transparency: transparent to translucent

·        Cleavage: none

·        Fracture: conchoidal

·        Streak: white

from (http://www.mineralminers.com/html/ameminfo.htm)
 

References

http://www.mineralminers.com/html/ameminfo.htm
http://www.minerals.net/mineral/silicate/tecto/quartz/varietys/amethyst.htm
http://www.colgandesigns.com/AmethystInformation.html
http://mineral.galleries.com/minerals/gemstone/amethyst/amethyst.htm