Shoshonite

Shoshonite is a basaltic rock, properly a potassic trachyandesite, composed of olivine, augite and plagioclase phenocrysts in a groundmass with calcic plagioclase and sanidine and some dark-colored volcanic glass. Shoshonite gives its name to the shoshonite series and grades into absarokite with the loss of plagioclase phenocrysts and into bannakite with an increase in sanidine. Shoshonite was named by Iddings in 1895 for the Shoshone River in Wyoming.