Anhydrous normal phosphate, fillowite group
Specific gravity: 3.35
Streak: Light brown
Colour: Dark brown
Johnsomervilleite is an accessory mineral in podiform metamorphic segregations in
Associated minerals include albite, bermanite,
triphylite and vivianite
At the Sapucaia mine, Sapucaia do Norte, Galiléia, Minas Gerais, Brazil, johnsomervilleite occurs as a primary mineral in a complex granite pegmatite in staurolite grade mica schist. Associated minerals include triphylite, frondelite, hureaulite, bermanite, jahnsite, rockbridgeite, phosphosiderite, vivianite, autunite, zircon, tourmaline, microcline, albite and quartz (HOM).
The type locality is Loch Quoich, Caol and Mallaig, Highland, Scotland, UK. Here johnsomervilleite occurs as one of several primary accessory minerals forming clusters in podiform metamorphic segregations in kyanite-sillimanite grade gneiss (HOM). The segregation pods consist of quartz, muscovite, plagioclase, almandine - spessartine garnet and apatite together with rare, very small clusters of graftonite, jahnsite, phosphosiderite, rockbridgeite, mitridatite, vivianite and johnsomervilleite. Johnsomervilleite usually occurs in close association with graftonite or vivianite. It is assumed that fairly high temperatures and pressures were operative during the formation of the primary phosphate assemblage (MM 43.331.833-836, HOM).
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