Phlogopite is favored in magnesium-rich rocks and in metamorphosed limestones. Where biotite is black or dark green, phlogopite is lighter brown or green or coppery. Click the photo for the full-sized version.
Phlogopite
The Mica Minerals
Phlogopite (FLOG-o-pite), KMg3AlSi3O10(OH,F)2, is biotite without the iron, and the two blend into each other in composition and occurrence. (more below)
Photo courtesy Woudloper via Wikimedia Commons
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