Sinkankasite Locality: Barker-Ferguson Mine, Keystone , Keystone District, Pennington County, South Dakota , USA ( Locality at mindat.org ) Size: miniature, 4.8 x 4.2 x 2.3 cm Sinkankasite A very rich and rare example of this rare phosphate species named after noted author and collector, John Sinkankas. I used to live down the street from him and he sold me a half dozen of these in the late 90s. Beyond that stash, I simply have not seen any good ones for sale since. This is extremely rare material, and hard to obtain today. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Sinkankasite
A hydrated manganese-aluminium phosphate named for gem author and collector John Sinkankas.
Intro adapted from Wikipedia (CC BY-SA).
Sinkankasite is an IMA-recognized mineral species in the phosphate class, with the chemical formula Mn²⁺Al(PO₃OH)₂(OH)·6H₂O.
It crystallizes in the triclinic crystal system (space group P-1).
Key properties: Mohs hardness 4; specific gravity 2.27; Vitreous to dull, vitreous on cleavages luster; optically biaxial.
IMA symbol Ska, IMA status: approved, named in 1982.
A late-stage hydrothermal alteration product of triphylite in complex zoned granite pegmatites.
It is found associated with Vivianite, huréaulite, carbonate-apatite, strengite, barbosalite, fluellite (Barker pegmatite, South Dakota, USA).
The mineral was named to honor Dr. John Sinkankas (1915–2002), American author and bibliographer on mineralogical and gemological subjects.