Thin section image of a lava sample from Yellowstone

Thin section image of a lava sample from Yellowstone using a polarizing microscope. The mineral assemblage is representative of many of Yellowstone’s basaltic rocks. The three large and colored crystals (known as phenocrysts) in the center of the image are the mineral olivine. The olivines are surrounded by a groundmass of small plagioclase feldspar crystals (white-grey blades) and micro-olivines (colorful specs). The black blebs within the olivine phenocrysts are inclusions of a mineral known as spinel.