Barker-Ferguson Mine, Keystone, Pennington Co., South Dakota (TYPE LOCALITY)
Miniature, 4.8 x 4.2 x 2.3 cm
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.