Robertsite , Beraunite Locality: Hagendorf South Pegmatite (Cornelia Mine; Hagendorf South Open Cut), Hagendorf , Waidhaus , Vohenstrauß , Oberpfälzer Wald , Upper Palatinate , Bavaria , Germany ( Locality at mindat.org ) Small reddish brown Robertsite spheres on Beraunite. Field of view 4mm. Specimen and photo Leon Hupperichs. — Photo: Leon Hupperichs · CC BY-SA 3.0
Robertsite
A secondary calcium-manganese phosphate named for South Dakota mineralogist Willard Roberts.
Intro adapted from Wikipedia (CC BY-SA).
Robertsite is an IMA-recognized mineral species in the phosphate class, with the chemical formula Ca₂Mn³⁺₃O₂(PO₄)₃·3H₂O.
It crystallizes in the monoclinic crystal system (space group A2/a). It is a member of the Arseniosiderite structural group.
Key properties: Mohs hardness 3.5; specific gravity 3.13–3.17; Chocolate-brown streak; Vitreous to resinous or waxy, silky in fibrous material luster; refractive index 1.805; optically biaxial.
IMA symbol Rbt, IMA status: approved, named in 1973.
A late secondary mineral in complex zoned granite pegmatites; in a phosphate deposit in limestone, derived from bat guano.
It is found associated with Rockbridgeite, ferrisicklerite, leucophosphite, jahnsite, montgomeryite, collinsite, huréaulite (Tip Top mine, South Dakota, USA); carbonate-fluorapatite.
The mineral was named to honor Professor Willard Lincoln Roberts (1923–1987), mineralogist, South Dakota School of Mines and Technology, Rapid City, South Dakota, USA.