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Amblygonite



Amblygonite

General
CategoryMineral
Chemical formula(Li,Na)AlPO4(F,OH)
Identification
ColorGenerally white or creamy, but can also be colorless or pale yellow, green, blue, beige, gray, brown or pink.
Crystal systemTriclinic
TwinningMicroscopic polysynthetic twinning common
Cleavage[100] Perfect, [110] Good, [011] Distinct
FractureIrregular/Uneven,Sub-Conchoidal
Mohs Scale hardness5.5 - 6[1]
LusterVitreous to pearly[1]
Polish lustergreasy to vitreous (in gem material)[1]
Refractive indexna=1.577 - 1.591,
nb=1.592 - 1.605,
nc=1.596 - 1.613
Optical PropertiesDouble refractive, biaxial, may be either positive or negative[1]
Birefringence.020 - .027[1]
Pleochroismweak to none[1]
Ultraviolet fluorescencevery weak green in long wave, light blue phosphorescence in long wave and short wave [1]
Specific gravity2.98 - 3.11
Other CharacteristicsPrismatic to columnar form

Amblygonite is a fluorophosphate mineral, (Li,Na)AlPO4(F,OH), composed of lithium, sodium, aluminium, phosphate, fluoride and hydroxide. The mineral occurs in pegmatite deposits and is easily mistaken for albite and other feldspars. Its density, cleavage and flame test for lithium are diagnostic. Amblygonite forms a series with montebrasite, the low fluorine endmember. Geologic occurrence is in granite pegmatites, high-temperature tin veins, and greisens. Amblygonite occurs with spodumene, apatite, lepidolite, tourmaline, and other lithium-bearing minerals in pegmatite veins. It contains about 10% lithium, and has been utilized as a source of lithium. The chief commercial sources have historically been the deposits of California and France.

Additional recommended knowledge

Contents

History

The mineral was first discovered in Saxony by August Breithaupt in 1817, and named by him from the Greek amblus, blunt, and gouia, angle, because of the obtuse angle between the cleavages. Later it was found at Montebras, Creuse, France, and at Hebron in Maine; and because of slight differences in optical character and chemical composition the names montebrasite and hebronite have been applied to the mineral from these localities. It has been discovered in considerable quantity at Pala in San Diego county, California; Caceres, Spain; and the Black Hills of South Dakota.

Gemology

Transparent amblygonite has been faceted and used as a gemstone. As a gemstone set into jewelry it is vulnerable to breakage and abrasion from general wear, as its hardness and toughness are poor.[1] The main sources for gem material are Brazil and the US. Australia, France, Germany, Namibia, Norway, and Spain have also produced gem quality amblygonite.[1]

References

  1. ^ a b c d e f g h i (Gia), Gemological. Gem Reference Guide. City: Gemological Institute of America (GIA), 1988. ISBN 0-87311-019-6
  • Klein, Cornelis and Hurlbut, Cornelius S., 1985, Manual of Mineralogy, 20th ed., p. 362, ISBN 0-471-80580-7
  • Mindat with location data
  • Webmineral data
  • Mineral Galleries

See also

 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Amblygonite". A list of authors is available in Wikipedia.
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