Augite Gneiss #192

Description

This rock was labelled a gneiss in the Ward’s Collection of Classic North American Rocks but shows little of the typical dark and light banding that defines a gneiss. The black (slightly greenish) mineral is diopside, the white mineral is plagioclase, and small amounts of hornblende are also present (but not easily seen without a microscope). The sample is from Lowell County, Idaho, USA. The sample is 8 cm across.