Formula: Li1-x(Fe3+,Mn2+)(PO4)
Anhydrous normal phosphate, forms a series with sicklerite
Specific gravity: 3.2 to 3.4
Hardness: 4
Streak: Light brown
Colour: Yellow-brown to dark brown
Solubility: Soluble in acids.

Hydrothermal environments

Ferrisicklerite is a secondary mineral which occurs only as a late hydrothermal alteration product of triphylite and lithiophilite in complex zoned granite pegmatites, commonly as rims around partly altered masses or crystals of the unaltered species (Mindat, Webmin, HOM).
Associated minerals include triphylite - lithiophilite, heterosite, alluaudite, phosphosiderite and cyrilovite (HOM).
Ferrisicklerite alters to the heterosite - purpurite series by oxidation of the Mn2+ to Mn3+ and leaching of the Li (Mindat, AM 22.875).

The type locality is Sidi Bou Othmane, Jebilet Mountain, Marrakech-Safi Region, Morocco.

At the Chickering mine, Cheshire county, New Hampshire, USA, ferrisicklerite is an alteration product of triphylite. It occurs together with heterosite where the parent triphylite has been hydrothermally altered (R&M 90.5.415-416).

At Rochester and North Groton, Strafford county, New Hampshire, USA, ferrisicklerite is found in pegmatites associated with hureaulite, stewartite, jahnsite and phosphosiderite (Dana).

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