This is an anorthosite, composed almost entirely of plagioclase (white). Pyroxene occupies the spaces between the plagioclase crystals. Although several thick layers of anorthosite exist in the Stillwater Complex, these rocks are rare, and how they form is poorly understood.
Topic: Earth Science
Subtopic: Earth Structure
Keywords: Anorthosite, Intrusions (Geology), Plagioclase, Pyroxene, Stillwater County (Mont.)