What is Phlogopite?

May. 25, 2021

Phlogopite is a common member of the mica mineral group. Its chemical composition is KMg32. The crystals of Phlogopite are usually brown, but can be yellow, green or reddish brown. It is sometimes referred to as "brown mica".

When phlogopite crystals are split into very thin flakes, these flakes are transparent, lustrous, chemically inert, tough, elastic, flexible and insulating. These and other properties of gold mica allow it to be used in the manufacture of a wide variety of products. Phlogopite and white mica are the only two mica minerals used commercially.

Geologic Occurrence

Phlogopite is usually found in metamorphic rocks. The ideal conditions for the formation of Phlogopite are those that cause dolomitic limestone or magnesium-rich limestone to undergo hydrothermal metamorphism.

The result is usually one of the following.

(A) scattered flakes and small crystals of aureole mica spread throughout the rock.

(B) Concentrations of phlogopite in clay-rich portions of the limestone.

(C) The concentration of phlogopite in shales metamorphosed along the limestone margins. Gold mica schist can be formed by the same process.

Phlogopite has also been found in igneous rocks. These include ultramafic rocks such as peridotite, kimberlite, sodalite and serpentinite. phlogopite is also found in high-alumina basalts. Almost all of the sheet and massive mica is found in pegmatites.

Physical properties of phlogopite

Phlogopite has a number of physical properties that can help you identify it. The first one is yellow to brown to reddish brown. Next, phlogopite, being a Mica, splits easily into transparent, soft, flexible and tough flakes.



Phlogopite crystals can be flat with a pseudo-hexagonal shape, or they can be barrel prisms with a pseudo-hexagonal cross section. Although phlogopite is a monoclinic mineral, the c-axis is so slowly tilted that it is easy to assume that the gold mica is hexagonal.

phlogopite has many properties that make it valuable in manufacturing. It can be sliced into thin sheets and can be used as electronic boards. They are hard but flexible and can be easily cut into shapes, punched or drilled. phlogopite is heat resistant, does not conduct electricity, and is a poor conductor of heat.

Uses of Phlogopite

Phlogopite and Muscovite Mica are the only two mica minerals used commercially. Phlogopite is used less than white mica because it is less available and because its brown color is undesirable for some applications. phlogopite is used in plastic composite body parts for automobiles. Phlogopite increases the stiffness of the plastic, provides greater dimensional stability, and reduces deformation during temperature changes.

Ground Phlogopite is used as an asbestos substitute for automotive brake and clutch pads. It is added to industrial coatings to improve strength, increase stiffness and improve resistance to heat, chemicals and UV light. It is an additive that increases the strength of epoxy resins, nylon and polyester.

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