Phlogopite

Phlogopite
General
CategoryMica, phyllosilicates
Formula
(repeating unit)
KMg3(AlSi3O10)(F,OH)2
IMA symbolPhl[1]
Strunz classification9.EC.20
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupC2/m
Identification
ColorBrown, brownish red, dark brown, yellow, yellowish brown, green, white and gray
Crystal habitTabular, scaly masses, rarely perfect phenocryst tablets
TwinningComposition twinning
CleavagePerfect basal (001)
FractureNone
TenacityTough, flexible thin laminae
Mohs scale hardness2–2.5
LusterPearly, sometimes slightly metallic on cleavage surfaces
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.78–2.85
Optical propertiesBiaxial (−), 2V=12
Refractive indexnα = 1.530–1.573 nβ = 1.557–1.617 nγ = 1.558–1.618
Birefringenceδ =0.0280–0.0450
2V angle16–20°
Other characteristicsFluorescent
References[2][3][4][5]

Phlogopite is a yellow, greenish, or reddish-brown member of the mica family of phyllosilicates. It is also known as magnesium mica.

Phlogopite is the magnesium endmember of the biotite solid solution series, with the chemical formula KMg3AlSi3O10(F,OH)2. Iron substitutes for magnesium in variable amounts leading to the more common biotite with higher iron content. For physical and optical identification, it has most of the characteristic properties of biotite.

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Mineralienatlas
  3. ^ Phlogopite WebMineral
  4. ^ http://rruff.geo.arizona.edu/doclib/hom/phlogopite.pdf Handbook of Mineralogy
  5. ^ http://www.mindat.org/min-3193.html Mindat