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(mineralogy) A mica mineral with the chemical formula KMg₃AlSi₃O₁₀(F,OH)₂, a basic potassium magnesium aluminosilicate, used as an insulator

Phlogopite – Phyllosilicate minerals, trioctahedral mica group, biotite subgroup – KMg₃(AlSi₃O₁₀)(F,OH)₂ – Phl – 9.EC.20 – Monoclinic – Prismatic (2/m) – (C2/m) – Brown, brownish red, dark brown, yellow, yellowish brown, green, white and gray – Tabular, scaly masses, rarely perfect phenocryst tablets – Composition twinning – Perfect basal (001) – None – Tough, flexible thin laminae – 2–2.5 – Pearly, sometimes slightly metallic on cleavage surfaces – White – Transparent to translucent – 2.78–2.85 – Biaxial (−), 2V=12 – Nα = 1.530–1.573 nβ = 1.557–1.617 nγ = 1.558–1.618 – Δ =0.0280–0.0450 – 16–20° – Fluorescent.

(mineralogy) A mica mineral with the chemical formula KMg₃AlSi₃O₁₀(F,OH)₂, a basic potassium magnesium aluminosilicate, used as an insulator

Phlogopite bearing peridotite from Finero, Italy. Coin of 1 Swiss franc (diameter 23 mm) for scale. The phlogopites are the glittering minerals surrounded by the green groundmass of olivine.