Amblygonite

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Amblygonite
File:Amblygonite-Quartz-Quartz-Calcite-171388.jpg
Amblygonite with quartz and calcite
General
Category	Phosphate minerals
Formula	(Li,Na)AlPO₄(F,OH)
Strunz classification	[[Strunz classification|]]
Dana classification	[[Dana classification|]]
Crystal system	[[Crystal system|]]
Crystal class
Color	White, colorless, pale yellow, greenish, bluish
Physical properties
Cleavage	Perfect on {001}, good on {110}
Mohs scale hardness
Luster	Vitreous, pearly on cleavages
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity
Optical properties
Refractive index
Crystal habit
Other characteristics

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Amblygonite is a phosphate mineral that is an important source of lithium. It is a lithium, sodium, aluminum phosphate with the chemical formula (Li,Na)AlPO₄(F,OH). The name "amblygonite" is derived from the Greek words "amblys" meaning "blunt" and "gonia" meaning "angle," referring to the mineral's obtuse cleavage angles.

Occurrence

Amblygonite is typically found in pegmatites, which are coarse-grained igneous rocks. It is often associated with other lithium-bearing minerals such as spodumene, lepidolite, and petalite. Notable localities for amblygonite include the Black Hills of South Dakota, USA; Minas Gerais, Brazil; and the Varuträsk pegmatite in Sweden.

Physical Properties

Amblygonite is a triclinic mineral, meaning it has three axes of unequal length that are not at right angles to each other. It has a perfect cleavage on the {001} plane and a good cleavage on the {110} plane. The mineral is brittle with an uneven fracture and has a Mohs hardness of 5.5 to 6. Its specific gravity ranges from 3.0 to 3.1.

The luster of amblygonite is vitreous, but it can appear pearly on cleavage surfaces. It is typically white or colorless, but can also be pale yellow, greenish, or bluish. Amblygonite is transparent to translucent and exhibits weak pleochroism.

Optical Properties

Amblygonite is biaxial (+) with refractive indices ranging from nα = 1.592 - 1.611, nβ = 1.596 - 1.612, and nγ = 1.602 - 1.622. It has a birefringence of δ = 0.010 - 0.011 and a measured 2V angle of 85° to 88°. The mineral displays weak pleochroism and has a dispersion of r < v.

Uses

Amblygonite is mined as a source of lithium, which is used in the production of lithium batteries, ceramics, and glass. It is also occasionally used as a gemstone, although its use in jewelry is limited due to its cleavage and brittleness.

Also see

• Spodumene
• Lepidolite
• Petalite
• Lithium
• Pegmatite