Amblygonite

Amblygonite
General
Category	Phosphate minerals
Formula (repeating unit)	(Li,Na)AlPO4(F,OH)
IMA symbol	Aby[1]
Strunz classification	8.BB.05
Crystal system	Triclinic
Crystal class	Pinacoidal (1) (same H-M symbol)
Space group	C1
Identification
Color	Generally white or creamy, but can also be colorless or pale yellow, green, blue, beige, gray, brown or pink.
Crystal habit	Prismatic to columnar form
Twinning	Microscopic polysynthetic twinning common
Cleavage	[100] Perfect, [110] good, [011] distinct
Fracture	Irregular/ineven, sub-Conchoidal
Mohs scale hardness	5.5–6[2]
Luster	Vitreous to pearly[2]
Specific gravity	2.98–3.11
Polish luster	greasy to vitreous (in gem material)[2]
Optical properties	Double refractive, biaxial, may be either positive or negative[2]
Refractive index	na=1.577 – 1.591, nb=1.592 – 1.605, nc=1.596 – 1.613
Birefringence	.020 – .027[2]
Pleochroism	weak to none[2]
Ultraviolet fluorescence	very weak green in long wave, light blue phosphorescence in long wave and short wave[2]

Amblygonite (/æmˈblɪɡəˌnaɪt/) 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.