Feldspar, from Tanzania (No.75)

The name feldspar derives from the German Feldspat, a compound of the words Feld, "field", and Spat, "a rock that does not contain ore". The change from Spat to -spar was influenced by the English word "spar", a synonym for "mineral". "Feldspathic" refers to materials that contain feldspar. The alternate spelling, felspar, has largely fallen out of use.

Feldspars are a group of rock-forming tectosilicate minerals that make up as much as 60% of the Earths crust.

Feldspars crystallise from magma as veins in both intrusive and extrusive igneous rocks and are also present in many types of metamorphic rock.