lithiophilite

(mineralogy) Li(Mn,Fe)PO₄ A salmon-pink or clove-brown mineral crystallizing in the orthorhombic system; isomorphous with triphylite.

Environment

A primary phosphate of complex pegmatite dikes, giving birth through alteration to a panoply of secondary phosphates.

Crystals rare, usually embedded and simple, commonly in solid masses of large crystal units without external faces. Triphylite is usually smaller, sharper, and more isolated; lithiophilite forms larger, cruder knots with altered rims and numerous secondary species.

Gray-blue to gray-blue-green (triphylite) or pinkish to greenish brown (lithiophilite). Luster glassy; hardness : 4Ɖ-5; specific gravity 3.4-3.6; streak white; fracture uneven to numerous small conchoidal patches; cleavage 1 fair and 2 imperfect. Brittle; transparent to barely translucent.

An isomorphous series of lithium, iron, and manganese phosphate (about 9.5% Li ₂ O, about 45% Fe ₂ O ₃ plus Mn ₂ O ₃ --both are always present--and about 45% P ₂ O ₅ ).

Fuse on charcoal to black bead, with lithiophilite fusing more readily than triphylite. Triphylite bead is magnetic. Crushed powder moistened with hydrochloric acid gives red lithium flame color. Moistened with sulfuric acid gives red lithium flash and then the continued blue-green flame of phosphorus.

The lithium flame coloration, with the dark color and the easy fusibility, distinguishes these from similar minerals. Their geological associations (pegmatite mineral) eliminate most other substances that might be confusing. In case of doubt, the chemical phosphorus test would be helpful.

Triphylite and lithiophilite are comparatively rare minerals, but are found in a number of pegmatites, which are in consequence called phosphate pegmatites. They may form tremendous irregular masses, often with secondary alteration products around their margins. Good crystals (triphylite) have been found at Chandler's Mill, Newport, New Hampshire. Great masses of both varieties are found at the Palermo quarry, North Groton, New Hampshire. Reported from Custer, South Dakota, and Pala, San Diego Co., California, in similar masses; some now-exhausted quarries and one active quarry (at Hagendorf) in Bavaria; from Rajasthan, India, and Mangualde, Portugal; and from several quarries in Rio Grande do Norte, Brazil, in great abundance.

Wherever these minerals occur, but especially with the manganese-rich variety lithiophilite, one may expect to find whole series of interesting phosphates derived from the alteration of the primary phosphate. Cracks and fissures in the fresh mineral are often lined with microscopic crystals of secondary phosphates. Branchville, Connecticut, became famous as a mineral locality because of the secondary phosphates formed from the lithiophilite found there (and its proximity to Yale geologists). The final stage in the alteration of lithiophilite is a black manganese oxide. This substance is likely to stain heavily such other species in phosphate-rich pegmatite and serve as a good guide to pegmatites of this makeup. Lithium-phosphate pegmatites are among the most rewarding localities for mineral collectors because the altering lithiophilite yields a wealth of colorful species.