amblygonite

n.
A white or greenish mineral, (Li,Na)Al(PO₄)(F,OH), that is an important source of lithium.

[German Amblygonit, from Greek amblugōnios, obtuse-angled : amblus, blunt + gōniā, angle.]

A lithium aluminum phosphate mineral of basic formula LiAl(PO₄F). The structure of amblygonite consists of phosphate (PO₄) groups of tetrahedra and AlO₆ groups of octahedra. Each PO₄ tetrahedron is connected to an AlO₆ octahedron. Amblygonite crystallizes in the triclinic system. Its color is commonly white or gray with tints of blue, green, and yellow. Amblygonite is transparent to translucent and has a vitreous to pearly luster.

The best-known occurrences of amblygonite are in Montebras, France; the Black Hills of South Dakota; the White Picacho District in Arizona; pegmatite districts in Maine; the Tanco pegmatite in Manitoba, Canada; and Portland, Connecticut. While amblygonite has been mined as an ore of lithium, it is not a major ore. See also Phosphate minerals.

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LiAl(PO
Triclinic -- pinacoidal

Environment

Lithium-bearing pegmatite dikes.

Crystal description

In its usual occurrence it forms medium to large embedded crystals with rough, irregular outlines. Now, however, being found in fine white and transparent crystals with numerous forms, several inches (to 20 cm) in length.

Physical properties

Colorless, yellow to white, light gray-green, lilac, or gray-blue. Luster glassy; hardness 5Ɖ-6; specific gravity 3.0-3.1; fracture uneven to subconchoidal; cleavage perfect basal, and interrupted cleavages on other planes. Brittle; transparent to translucent; often fluorescent, weakly orange in longwave ultraviolet light.

Composition

Basic lithium aluminum fluophosphate (10.1% Li ₂ O, 34.5% Al ₂ O ₃ , 48.0% P ₂ O ₅ , 12.8% F, but some of the F replaces O, 5.4% of O equals F).

Tests

Fuses easily to white porcelaneous sphere that fluoresces white in shortwave ultraviolet light. Acid on powder gives red lithium flame. Dissolves in acid to give a good phosphorus test.

Distinguishing characteristics

In pegmatites it might be confused with feldspar, from which it is easily distinguished by its fusibility. A difference in luster is apparent to the trained eye.

Occurrence

Amblygonite is a mineral of complex pegmatites and may be abundant locally, occurring in large masses embedded in quartz or feldspar. Such masses are found in Ceara, Brazil, where it almost seems to substitute for the feldspar of a dike. It is found similarly in pegmatites in Sweden, Western Australia, the Black Hills of South Dakota, California (Pala), and Maine. Although a potential source of lithium, it is not now used for that purpose to any extent. The Newry (Maine) occurrence of well-formed, colorless, and transparent to milky white crystals is apparently a late stage of pegmatite formation--later than is usually the case with this mineral. In normal occurrences the amblygonite is embedded in other minerals and is only crudely formed into crystals. Brazil appears to have at least two good occurrences in Minas Gerais, near Governador Valadares. Gemmy yellow crystals as much as 4 in. (10 cm) across characterize one source; elongated, flattened twins as much as 6 in. long, 1 in. wide, and ƈ in. thick (15 × 2 × 0.5 cm) come from the other locality (Mendes Pimentel).

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The noun has one meaning:

Meaning #1: a white or gray mineral consisting of lithium aluminum phosphate; a source of lithium

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