Dark brown crystals of the rare phosphate mineral jonhsomervilleite from Minas Gerais (Sapucaia Mine, Sapucaia do Norte, Galiléia, Minas Gerais, Brazil). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Johnsomervilleite
Johnsomervilleite is an IMA-recognized mineral species in the phosphate class, with the chemical formula Na₃CaFe²⁺₁₁(PO₄)₉.
It crystallizes in the hexagonal crystal system. It is a member of the Fillowite structural group.
Key properties: Mohs hardness 4.5; specific gravity 3.35; Pale brown; gray-brown with an olive tint streak; Vitreous luster; optically biaxial.
IMA symbol Jsv, IMA status: approved, named in 1979.
Occurs as one of several primary accessory minerals forming clusters in podiform metamorphic segregations in kyanite-sillimanite-grade gneiss (Loch Quoich, Scotland).
It is found associated with Graftonite, apatite, jahnsite, phosphosiderite, vivianite, rockbridgeite, mitridatite, almandine-spessartine, muscovite, plagioclase, quartz (Loch Quoich.
The mineral was named to honor John M. Somerville (1908–1978), who collected the first specimens.