Outstanding sharp brown crystals of the extremely rare Ca-Mn-phosphate mineral pararobertsite from the TL in Tip Top mine and the only confirmed locality worldwide (Tip Top Mine, Fourmile, Custer County, South Dakota, United States of America). Ex Vandenbroucke Museum collection from Waregem, Belgium. — Photo: David Hospital · CC BY-SA 4.0
Pararobertsite
Pararobertsite is an IMA-recognized mineral species in the phosphate class, with the chemical formula Ca₂Mn³⁺₃(PO₄)₃O₂·3H₂O.
It crystallizes in the monoclinic crystal system (space group P2_1/c).
Key properties: specific gravity 3.22; Brownish red streak; Vitreous luster; optically biaxial.
IMA symbol Prb, IMA status: approved, named in 1987.
Found as a rare secondary mineral in a complex zoned granite pegmatite.
It is found associated with Whitlockite, carbonate-apatite, quartz.
Its name comes from the Greek para, for near, and its relation to robertsite.