Phlogopite
Potassium Iron Magnesium Aluminum Silicate Fluoride Hydroxide, K(Mg,Fe)3(AlSi3)O10(F,OH)2
Crystal System: Monoclinic
Hardness: 2.5-3.0
Density: 2.86

Phlogopite is a member of the mica group that occurs in magnesium rich metamorphic rocks such as serpentinites, crystalline dolomites and altered peridotites. It commonly occurs as plates in kimberlites and in pegmatites and contact limestones.

Phlogopite occurs as tabular crystals and as short pseudo-hexagonal prisms. It also occurs as lamellar or foliated aggregates or disseminated flakes. Six sided plates as large as 2 meters across are known to occur. Phlogopite crystals vary in color from yellowish to reddish brown to gray with a vitreous to submetallic luster, and sometimes exhibit a coppery appearance. Some specimens exhibit a striking transparency.

Phlogopite finds use as an industrial mineral, and plates of it have been historically used in applications that take advantage of this mica group mineral's properties as an electrical insulator. It also finds applications in powder form as a filler.

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bkeller@rockhounds.com 11/6/95