MICA REMAINS IMPORTANT INDUSTRIAL MINERAL
Harold Hough              

            Usually seen as a mineral curiosity on the side of a trail, mica has been a major industrial mineral and remains so, even though technology has overcome some of its advantages.  It’s used in construction, energy production, and even electrical power generation.
            Mica is actually a group of silicate minerals that have nearly perfect cleavage – that is that it can easily be separated into sheets.  There are several types including biotite, muscovite, lepidolite, and phlogopite.  It ranks as one of the first minerals used.  The earliest use of mica has been found in cave paintings created during the Upper Paleolithic period (40,000 BC to 10,000 BC).  White hues in the paint were from kaolin or mica.
            Mica’s uses grew.  Although glass was a popular medium for windows, Mica was often mined and used in remote territories where it was too expensive to ship glass windows.  This made large mica crystals expensive because of demand and it wasn’t until the early 19th century when discoveries in Africa and South America made it more affordable.
            Mica also had advantages over glass.  Since it was heat resistant and transparent, it was used in lanterns, and windows in furnaces and wood stoves.  Since it was also flexible, it was used in windows of wooden ships and lanterns for horse drawn carriages, where glass would break under the vibrations and expansion and contractions from changing temperatures.  In 1840, when gold cost $25 an ounce, mica sold for about $2 a pound.  Today, the highest quality mica can go for $1000 a pound!
            Mica also has other qualities.  It is light, chemically inert, thermally stable, elastic, hydrophilic, reflective and an electric insulator.  Although plastics are regularly used in insulators, mica is still used in areas with high voltages (and therefore higher temperatures), critical wiring in defense systems and places where high temperatures could damage regular insulation.  Specific high-temperature mica-insulated wire and cable is rated to work for up to 15 minutes in molten aluminum, glass, and steel.
            Although sheet mica isn’t used for regular windows anymore, it is still used in fields where its unique characteristics are required.  It is still used in stove and kerosene heater windows.  Since it is relatively transparent to radiation (such as alpha particles) while being impervious to most gases, it is used as a window on radiation detectors such as Geiger counters.
            Although we think of mica as a sheet mineral, even ground up mica has applications.  Ground mica is used in the well-drilling industry as an additive to drilling fluids. The coarsely ground mica flakes help prevent the loss of circulation by sealing porous sections of the drill hole. Well drilling muds accounted for 15% of dry-ground mica use in 2008.
            Since mica is inert, it is frequently used as filler, especially in parts for automobiles as lightweight insulation to suppress sound and vibration. Mica is used in plastic automobile fascia and fenders as a reinforcing material, providing improved mechanical properties and increased dimensional stability, stiffness, and strength. Mica-reinforced plastics also have high-heat dimensional stability, reduced warpage, and the best surface properties of any filled plastic composite.  Half of the ground mica is used as a joint compound and another quarter is used as a additive to paint.
            Since mica has a “platey” nature, it is also often used a mold release compound for rubber products like tiers.  It also counteracts the stickiness of asphalt in roof shingles.
            America is the third largest producer of mica.  One American mica mining company is the Quartz Corporation.    Their mining operation in Spruce Pine, NC produces some of the largest feldspar and mica crystals even though their major mica product is ground mica.
            Fortunately, mica is one mineral that can be found domestically in sufficient quantities.  It is a strategic mineral according to the Defense Department and there is a small, but steady export market for it.