Robertsite

Robertsite (Ca6Mn3+9(PO4)9O6(H2O)6·3H2O) or Ca2(Mn3(PO4)3O2)(H2O)3 or is a secondary phosphate species named for Willard Lincoln Roberts (1923-1987), mineralogist and professor who taught at South Dakota School of Mines in Rapid City, South Dakota. The type locality for Robertsite is the Tip Top mine, Custer County, South Dakota, USA.

Robertsite occurs at the Tip Top Mine as minute crystal aggregates and crusts found on quartz associated with Triphylite dark reddish brown to black in color.