Phlogopite with pen for scale. From the mineral collection of Brigham Young University Department of Geology, Provo, Utah, courtesy of the U.S. Geological Survey Denver Library Photographic Collection. (Photo by Andrew Silver.)

Formula: KMg3(AlSi3O10)(OH)2 Monoclinic


Phlogopite is a tan mica found most often in magnesium-rich rocks such as marbles, calc-silicate and ultramafic rocks.

KENOSHA COUNTY: Phlogopite occurs in a subsurface, diamond-bearing lamprophyre diatreme, discovered within the outskirts of Kenosha (Carlson and Adams, 1997).

ONEIDA COUNTY: Phlogopite occurs in some of the sulfide-rich metamorphosed carbonate rocks in the Lynne massive sulfide deposit. Associated minerals are talc, chlorite, pyrite, pyrrhotite and galena (Adams, 1996).