U.S. Geological Survey

Monday, November 3, 2014

Jason Christopher Willett, a mineral commodity expert at the U.S. Geological Survey, compiled the following information about mica.

Mica was discovered in 1803 at the Ruggles Mine in Grafton, New Hampshire. Image source: ©James St. John, CC BY 2.0.

The mica mineral group includes 34 kinds of layered silicate minerals, all of which have a layered and plate-like texture. This mineral has been known for thousands of years: Mica was first mined in India about 4,000 years ago and is mainly used in medicine. The Maya used it as a decoration in the plaster, making their temples sparkle in the sun. Today, it is used in everything from electronics to cosmetics.

Mica is highly reflective, and its excellent cleavage causes it to split into thin slices; these tough and flexible thin slices are the distinguishing feature of this mineral group. The flakes are transparent, if the color is darker, they are translucent. Mica is stable when exposed to electricity, light, humidity and extreme temperatures.

Commercial forms of mica can be classified as unmanufactured or manufactured. Unprocessed mica can be divided into flake mica and waste mica, including flake mica. Most of the formed or stamped mica is used in electrical products.

The main mica minerals used in commercial applications are biotite, muscovite and phlogopite. Biotite is usually used as a soil additive in its ground (granular) form; muscovite and phlogopite are applied in flake and ground form. Muscovite flake mica can only be recovered from pegmatite deposits; phlogopite flake mica is recovered from pyroxene.

Muscovite is the main mica used in the electrical industry to make mica-based capacitors that can operate at temperatures or frequencies that are destructive to polypropylene capacitors. Phlogopite is used in plastic composite materials for automotive applications due to its dimensional stability, increased stiffness and improved heat distortion temperature.

Artificial mica includes composite mica, glass-bound mica, ground mica, phosphate-bound mica and recombinant mica. Waste mica refers to materials that are below the specifications of flake mica due to substandard size, color or quality. Most waste mica is used as the raw material for two kinds of ground mica: wet grinding and dry grinding.

Dry milled mica is a finely divided, rough material, the flakes of which show considerable surface damage and lack luster. It is used in joint compounds to bond, strengthen and fill the joints between drywall panels; as a substitute for asbestos in automotive products; prevent adhesion in roof tile coatings; and insulate against high temperatures and ultraviolet radiation.

Wet milled mica is a finely divided material whose flakes have smooth rounded edges and maintain their luster. Wet-ground mica retains the brilliance of its cleavage surface and is mainly used in pearlescent coatings in the automotive industry, but its reflection and refraction properties make it an important ingredient in cosmetics, from eyeliner and eye shadow to body glitter, lipstick and nail polish.

For more information about mica and other mineral resources, please visit: minerals.usgs.gov/minerals.

In 2013, the United States produced approximately 48,000 metric tons of crushed mica and flake mica, and approximately 79,000 metric tons of mica powder.

The world's annual production of mica is estimated to be 1.12 million tons.

Many countries have waste and flake mica resources. The largest producers are China, Finland, India, Madagascar, South Korea, Turkey, Russia and the United States.

"Mica" was originally a Latin word meaning "bread crumbs".

In 1803, the United States discovered mica at the Ruggles Mine in New Hampshire; mining began shortly after, and the mica was exported to the United Kingdom for household products.

White mica flakes are used as snowflakes in Christmas decorations.

Mica flakes are used to make isinglass boards and are used as observation windows in coal, kerosene and wood burning furnaces.

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