Fluorophlogopite

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Formula: KMg₃(Si₃Al)O₁₀F₂
Phyllosilicate (sheet silicate), biotite subgroup, mica group
Crystal System: Monoclinic
Specific gravity: 2.83 calculated
Hardness: 2 to 3
Streak: White
Colour: Pale yellow
Environments

Volcanic igneous environments
Metamorphic environments

Localities

At the Fiano tuff quarries, Nocera Inferiore, Salerno, Campania, Italy, fluorine, boron and magnesium rich metamorphosed xenoliths occur in the ignimbrite deposits. These rocks originated from limestone embedded in a fluid flow. Some of the xenoliths consist of fluorophlogopite-bearing calc-silicate rocks. They are composed of abundant fluorophlogopite, widespread fluorite, fluorine-rich chondrodite, fluoborite, diopside, Fe(Mg)-oxides, calcite, humite, potassium-bearing fluoro-richterite and grossular. It appears that steam enriched in fluorine, boron, magnesium and arsenic infiltrated carbonate rocks at a temperature of about 300 to 450°C during the emplacement of the ignimbrite (MM 81.1165-1189).

At the type locality, Mt Calvario, Biancavilla, Etna Volcanic Complex, Metropolitan City of Catania, Sicily, Italy, fluorophlogopite occurs in metasomatised lava as very thin, flat laminae with a diameter of 200–400 microns. Associated minerals include fluoro-edenite, K-feldspar, clinopyroxene, orthopyroxene, fluorapatite, hematite and pseudobrookite (AM 92.1602-1609).

At the ZCA No. 3 Mine, Balmat, Balmat-Edwards Zinc Mining District, St. Lawrence county, New York, USA, fluorophlogopite occurs in siliceous marble. One sample consists of fluorophlogopite, tremolite, diopside, calcite, quartz, graphite, scapolite, plagioclase, pyrite, pyrrhotite, chalcopyrite and fluorapatite. A second generation of tremolite occurs as rims on diopside and minor dolomite is concentrated at calcite grain boundaries. Another sample consists of fluorphlogopite, fluorine-rich tremolite, calcite and norbergite. Minor graphite, pyrite, fluorapatite and sphalerite are also present as well as minor retrograde dolomite concentrated at calcite grain boundaries (AM 67.545-557).

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