Lipscombite

minerals

barbosalite

cyrilovite

frondelite

Formula:Fe2+Fe3+2(PO4)2(OH)2
Anhydrous phosphate containing hydroxyl, paramorph of barbosalite
Specific gravity: 3.66 AM 47.353
Colour: Green-grey, olive green, black
Environments

Pegmatites

Lipscombite is a very rare phosphate, originally known as a synthetic mineral.

At the type locality, the Sapucaia mine, Sapucaia do Norte, Galiléia, Minas Gerais, Brazil, lipscombite occurs in vugs in the hydrothermally altered phosphate zone of a complex granite pegmatite, intimately intergrown with cyrilovite, leucophosphite, phosphosiderite, and frondelite (Webmin, HOM, Dana).
Manganoan lipscombite from this locality contains a significant substitution of manganous manganese for ferrous iron. Both the tetragonal (lipscombite) and monoclinic (barbosalite) forms of (Fe2+, Mn2+)Fe3+2(PO4)2(OH)2 occur here. Lipscombite is apparently limited in its occurrence to an alkali-altered oxidised zone in frondelite, into which cyrilovite has been introduced. Barbosalite is apparently limited in its occurrence to triphylite and heterosite rock, being particularly abundant along solution channels where it occurs admixed with nonoxidised minerals such as triphylite, hureaulite and vivianite, and with oxidised minerals such as heterosite and tavorite. It appears that the acidity (pH) of the solutions may be one factor in determining whether manganoan lipscombite or barbosalite may form.
Lipscombite occurs admixed with cyrilovite and leucophosphite; the latter replace frondelite and require a source of sodium and potassium ions for their formation and hence are probably formed in an alkaline environment; barbosalite occurs associated with hureaulite, an acid phosphate with a deficiency of metal cations suggesting an acid environment for the formation of barbosalite. The presence of cyrilovite as a"seed" crystal may also influence the growth of manganoan lipscombite since both cyrilovite and manganoan lipscombite are intimately intergrown, cyrilovite occurring free of lipscombite, but lipscombite not occurring independently of cyrilovite.
The monoclinic paramorph, barbosalite, when formed, changes to lipscombite between 110 and 290oC; the transformation is sluggish and is accompanied by oxidation of iron (AM 47.353-359).

At Hagendorf, Germany, lipscombite is associated with heterosite, strengite, cyrilovite and leucophosphite (HOM).

Alteration

Synthetic ferrous ferric lazulite changes to lipscombite between 110 and 290oC. Above 290oC lipscombite contains no divalent iron. It changes to "iron berlinite" (FePO4) and hematite around 560oC, above which an unknown compound forms at the expense of both hematite and "iron berlinite". If ferrous phosphate is only partially oxidised, lipscombite is obtained. However, if ferrous phosphate is heated in air, it is dehydrated and oxidised to an amorphous ferric phosphate below 110oC. This product crystallises at about 560oC to hematite, a ferric orthophosphate and the unknown compound mentioned above. The ferric orthophosphate is converted to "iron berlinite" below 650oC (AM 38.612-638).

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