Mineral: sanbornite Locality: Incline (Mariposa County), California Size: 5 x 4 x 3 cm Sanbornite, a rare barium feldspar. The white sanbornite crystals in this sample are on the left side and center of the photo. The surrounding matrix is composed of quartz (white at the bottom of the photo) and celsian (transparent grayish masses). — Photo: Astynax · Public domain
Sanbornite
A rare barium phyllosilicate — colorless-to-green orthorhombic plates.
Intro adapted from Wikipedia (CC BY-SA).
Sanbornite is an IMA-recognized mineral species in the silicate class, with the chemical formula BaSi₂O₅.
It crystallizes in the orthorhombic crystal system (space group Pcmn).
Key properties: Mohs hardness 5; specific gravity 3.7; Pearly luster; refractive index 1.612; optically biaxial.
IMA symbol Sabn, grandfathered status — known before the IMA’s founding, named in 1932.
Found in veins in metamorphosed sediments, largely quartzites and hornfels (Trumbull Peak, California, USA).
It is found associated with Quartz, gillespite, diopside, schorl, celsian, pyrrhotite, witherite (Trumbull Peak, California, USA); gillespite, pellyite, taramellite, fresnoite, muirite.
The name refers to Frank Sanborn (1862–1936), mineralogist with the California Division of Mines, San Francisco, California, USA.