Home Minerals Phlogopite


Phlogopite is a member of mica group family of phyllosilicates mineral. Color is a yellow, greenish, or reddish-brown. It is the magnesium endmember of the biotite stable answer series, with the chemical formulation KMg3AlSi3O10 (F, OH) 2. Iron substitutes for magnesium in variable quantities main to the more commonplace biotite with higher iron content. For physicaly and optical identification, it shares most of the feature of biotite.

An extensive-unfold member of the mica group occurring particularly in crystalline, dolomitic marbles associated with spinel, diopside and members of the chondrodite organization. Redefined as the OH give up-member via the IMA Mica Subcommittee in 1998.

May additionally alter to vermiculite.

Name: From the Greek for firelike, referring to an oft-seen reddish tint.

Association: Dolomite, calcite, diopside, tremolite, scapolite, vesuvianite, apatite, titanite, epidote, olivine, augite, magnetite.

Polymorphism & Series: 1M, 2M1 ; 3A polytypes; forms a series with biotite

Mineral Group: Mica group

Crystallography: Monoclinic; prismatic. Usually in six-sided plates or in tapering prismatic crystals. Crystals frequently large and coarse. Found also in foliated masses

Phlogopite Composition: A hydrous potassium magnesium aluminum silicate, KMg2Al2Si3Oio(OH)2. Usually contains about 3 percent of fluorine and some iron.

Diagnostic Features: Characterized by its micaceous cleavage and yellowish brown color. Distinguished from muscovite by its decomposition in sulfuric acid and from biotite by its lighter color. But it is impossible to draw a sharp distinction between biotite and phlogopite.

Phlogopite Uses: Same as for muscovite; chiefly as electrical insulator.

Chemical Properties

Chemical Classification Phyllosilicates, Mica
Formula KMg3(AlSi3O10)(F,OH)2
Common Impurities Mn,Ba,Cr,Na,Ti,Ni,Zn,Ca,Li,Rb,H2O

Phlogopite Physical Properties

Crystal habit Tabular, scaly masses, rarely perfect phenocryst tablets
Color Brownish red, dark brown, yellowish brown, green, white
Streak White
Luster Vitreous, Pearly
Cleavage Perfect on {0001}
Diaphaneity Transparent, Translucent
Mohs Hardness 2 – 3
Crystal System Monoclinic
Tenacity Flexible
Density 2.78 – 2.85 g/cm3 (Measured)    2.79 g/cm3 (Calculated)
Fracture Micaceous
Other characteristics Fluorescent

Phlogopite Optical Properties

Color / Pleochroism Visible
2V: Calculated: 16° to 20°
RI values: nα = 1.530 – 1.573 nβ = 1.557 – 1.617 nγ = 1.558 – 1.618
Twinning Composition twinning
Optic Sign Biaxial (-)
Birefringence δ = 0.028 – 0.045
Relief Moderate
Dispersion: r < v distinct

Occurrence of Phlogopite

Phlogopite occurs as a product of metamorphism in crystalline magnesium limestones or dolomitic marbles and is also found in serpentine. Rarely found in igneous rocks. Notable localities are in Finland; Sweden; Campolungo, Switzerland; Ceylon; Madagascar. In the United States found chiefly in Jefferson and St. Lawrence Counties, New York. Found abundantly in Canada in Ontario at North and South Burgess, and in various other localities in Ontario and Quebec.


Some localities for well-crystallized material include:

  • In the USA, from Antwerp and Natural Bridge, Jefferson Co., and Edwards and Pierrepont, St. Lawrence Co., New York; from Franklin, Sussex Co., New Jersey.
  • In Canada, large crystals from the Lacey mine, Frontenac Co., and in North and South Burgess Townships, Ontario; from near Perkin’s Mills, and elsewhere in Gatineau Co., Quebec.
  • In the Slyudyanka region, near Lake Baikal, Siberia, Russia.
  • At near Feset, Norway.
  • From Campolungo, near St. Gotthard, Ticino, Switzerland.
  • In the Val di Fassa, Trentino-Alto Adige, and on Monte Braccio, Val Malenco, Lombardy, Italy.
  • From Saharakara and Ampandrandava, Madagascar.
  • At Anxiety Point, Nancy Sound, New Zealand.


  1. Bonewitz, R. (2012). Rocks and minerals. 2nd ed. London: DK Publishing.
  2. Dana, J. D. (1864). Manual of Mineralogy… Wiley.
  3. Handbookofmineralogy.org. (2019). Handbook of Mineralogy. [online] Available at: http://www.handbookofmineralogy.org [Accessed 4 Mar. 2019].
  4. Mindat.org. (2019): Mineral information, data and localities.. [online] Available at: https://www.mindat.org/ [Accessed. 2019].A