Hydrated phosphate containing hydroxyl, leucophosphite group
Specific gravity: 2.69
Colour: Deep red, colourless
At the type locality, the Tip Top Mine, Fourmile, Custer Mining District, Custer county, South Dakota, USA, tinsleyite is moderately abundant, and is found in highly altered triphylite pods within the intermediate zone of the pegmatites. This zone consists of large feldspar variety perthite crystals with quartz, muscovite, fluorapatite, albite, beryl, minor elbaite and columbite-tantalite. In most cases, the triphylite has been totally altered to secondary phosphates. Rockbridgeite-frondelite and tavorite are among the earliest secondary phosphates formed with rockbridgeite being dominant. Leucophosphite crystals about 5 mm in length formed subsequent to rockbridgeite-frondelite and tavorite. Tinsleyite formed after leucophosphite on which it commonly occurs as morphologically continuous overgrowths. Spherical aggregates of robertsite, together with prismatic crystals of a jahnsite-group mineral, formed subsequent to leucophosphite and tinsleyite. Other minerals younger than tinsleyite include carbonate-rich apatite and laueite (AM 69.374-376).
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