Amblygonite is a fluorophosphate mineral, (Li,Na)AlPO4(F,OH), composed of lithium, sodium, aluminium, phosphate, fluoride and hydroxide. The mineral occurs in pegmatite deposites and is easily mistaken for albite and other feldspars. Its density, cleavage and flame test for lithium are diagnostic. Geologic occrrence 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.
Properties
| Crystallographic system
| Triclinic
|
| Form
| Prismatic to columnar
|
| Twinning
| Microscopic polysynthetic twinning common
|
| Colors
| Generally white or creamy, but can also be colorless or pale yellow, green, blue, beige, gray or pink.
|
| Luster
| Vitreous to pearly
|
| Hardness
| 5.5 - 6
|
| Specific gravity
| 2.98 - 3.11
|
| Refractive index
| na=1.577 - 1.591 nb=1.592 - 1.605 nc=1.596 - 1.613
|
| Cleavage
| [100] Perfect, [110] Good, [011] Distinct
|
| Fracture
| Irregular/Uneven,Sub-Conchoidal
|
History
The mineral was first discovered in Saxony by A. 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.
References