Phlogopite
A phlogopite crumbled cleavage plate Image File history File links Download high resolution version (652x626, 169 KB) File links The following pages link to this file: Phlogopite User:Aramgutang/Gallery Categories: User-created public domain images ...
General
Category	Mineral
Chemical formula	K(Mg,Fe,Mn)3Si3AlO10(F,OH)2)
Identification
Colour	Yellowish- or greenish-brown
Crystal habit	Tabular, scaly masses, rarely perfect phenocryst tablets
Crystal system	Monoclinic
Cleavage	Perfect basal
Fracture	Bends without breaking
Mohs Scale hardness	2 to 2.5
Luster	Pearly, sometimes slightly metallic
Refractive index	Transparent
Pleochroism	None
Streak	Colorless

Phlogopite is a yellow, greenish or reddish brown member of the mica family of phyllosilicates. It is also known as magnesium mica. Minerals are natural compounds formed through geological processes. ... A chemical formula (also called molecular formula) is a concise way of expressing information about the atoms that constitute a particular chemical compound. ... In mineralogy, shape and size give rise to descriptive terms applied to the typical appearance, or habit of crystals. ... Rose des Sables (Sand Rose), formed of gypsum crystals In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... In crystallography, the monoclinic crystal system is one of the 7 lattice point groups. ... Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite planes, creating smooth surfaces, of which there are several named types: Basal cleavage: cleavage parallel to the base of a crystal, or to the plane of the lateral axes. ... A fracture is the separation of a body into two, or more, pieces under the action of stress. ... Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. ... The refractive index (or index of refraction) of a material is the factor by which the phase velocity of electromagnetic radiation is slowed in that material, relative to its velocity in a vacuum. ... Pleochroism is an optical phenomenon where due to double refraction of light by a colored gem or crystal, the light is divided into two paths which are polarized at a 90° angle to each other. ... Minerals are natural compounds formed through geological processes. ... rock with mica Mica sheet mica flakes The mica group of minerals includes several closely related materials having highly perfect basal cleavage. ... The silicate minerals make up the the largest and most important class of rock-forming minerals. ... General Name, Symbol, Number magnesium, Mg, 12 Chemical series alkaline earth metals Group, Period, Block 2, 3, s Appearance silvery white Atomic mass 24. ...

Phlogopite is the magnesium endmember of the biotite solid solution series, with the chemical formula KMg ₃AlSi₃O₁₀(F, OH)₂. A Biotite slice Biotite is a common phyllosilicate mineral that contains potassium, magnesium, iron and aluminium. ... A binary phase diagram displaying solid solutions over the full range of relative concentrations. ...

For physical and optical identification, it shares most of the characteristic properties of the more common biotite, being distinguished from it by having a lighter colour with a hint of olive green.

Paragenesis

Phlogopite is an important and relatively common end-member composition of biotite. Phlogopite micas are found primarily in igneous rocks, although it is also common in contact metamorphic aureoles of intrusive igneous rocks with magnesian country rocks.

The occurrence of phlogopite mica within igneous rocks is difficult to constrain precisely because the primary control is rock composition as expected, but phlogopite is also controlled by conditions of crystallisation such as temperature, pressure and vapour content of the igneous rock. Several igneous associations are noted; high-alumina basalts, ultrapotassic igneous rocks, and ultramafic rocks.

Basaltic association

The basaltic occurrence of phlogopite is in association with picrite basalts and high-alumina basalts. Phlogopite is stable in basaltic compositions at high pressures and is often present as partially resorbed phenocrysts or an accessory phase in basalts generated at depth.

Ultrapotassic association

Phlogopite mica is a commonly known phenocryst and groundmass phase within ultrapotassic igneous rocks such as lamprophyre, kimberlite, lamproite and other deeply-sourced ultramafic or high-magnesian melts. In this association phlogopite can form well preserved megacrystic plates to 10cm, and is present as the primary groundmass mineral, or in association with pargasite amphibole, olivine and pyroxene. Phlogopite in this association is a primary igneous mineral present because of the depth of melting and high vapour pressures. Lamprophyres (Greek Lampros, bright, and the terminal part of the word porphyry, meaning rocks containing bright porphyritic crystals) are a group of rocks containing phenocrysts, usually of biotite and hornblende (with bright cleavage surfaces), often also of olivine and augite, but not of feldspar. ... Hewn kimberlite core sample from the James Bay Lowlands region of Northern Ontario, Canada. ... Lamproite is a peralkaline volcanic rock. ...

Ultramafic rocks

Phlogopite is often found in association with ultramafic intrusions as a secondary alteration phase within metasomatic margins of large ultramafic to mafic layered intrusions. In some cases the phlogopite is considered to be produced by autogenic alteration during cooling. In other instances, metasomatism has resulted in phlogopite formation within large volumes, as in the ultramafic massif at Finero, Italy, within the Ivrea Zone. Trace phlogopite, again considered the result of metasomatism, is common within coarse-grained peridotite xenoliths carried up by kimberlite, and so phlogopite appears to be a common trace mineral in the uppermost part of the Earth's mantle. Metasomatism is the chemical alteration of a rock by hydrothermal fluids. ... It has been suggested that this article or section be merged with Ultramafic intrusion. ... Metasomatism is a geologic process where metamorphism causes an alteration in a mineral or rock mass that involves a chemical change of the substance with the addition of material, as when chrysolite (olivine) is converted to serpentine basically by the addition of water. ... Peridotite Peridotite is a dense, coarse-grained rock, consisting mostly of the minerals olivine and pyroxene. ... The xenolith (Greek: foreign rock) is a rock which becomes enveloped in a larger rock during the latters development and hardening. ... Hewn kimberlite core sample from the James Bay Lowlands region of Northern Ontario, Canada. ... Earth cutaway from core to exosphere. ...

References

• Deer, W.A., R.A. Howie, and J. Zussman (1963) Rock-forming minerals, v. 3, sheet silicates, p. 42-54
• Mineral Data Publishing, 2001 PDF
• MinDat entry
• Webmineral data