Natural resources are the foundation for our lives and lifestyles.
What would our lives be like without mining? Imagine a world without transportation such as jet planes or railroads, without communications such as cell phones or radar, without decorative items such as art or jewelry, without buildings such as skyscrapers or parking garages, without defense systems items such as missiles or submarines, without medical care items such as X-rays or surgical tools. We wouldn’t have any of these things without mining and minerals.
Mica is a mineral name given to a group of minerals that are physically and chemically similar. They are all silicate minerals, known as sheet silicates because they form in distinct layers. Micas are fairly light and relatively soft, and the sheets and flakes of mica are flexible. Mica is heat-resistant and does not conduct electricity. There are 37 different mica minerals. The most common include: purple lepidolite, black biotite, brown phlogopite and clear muscovite.
Mineral Classification: silicates
Lepidolite K(Li,Al)3(AlSi3O10) (O,OH, F)2, ; biotite K(Mg, Fe)3(AlSi3O10) (OH)2; phlogopite KMg3(AlSi3O10) (OH)2; muscovite KAl2(AlSi3O10)(OH)2
Crystal System: monoclinic
Color: purple, rosy, silver, gray (lepidolite); dark green, brown, black (biotite); yellowish-brown, green white (phlogopite); colorless, transparent (muscovite)
Luster: pearly, vitreous
Streak: White, colorless
2.5-4 (lepidolite); 2.5-3 biotite; 2.5-3 phlogopite; 2-2.5 muscovite
The mica industry can be divided into two distinct but interdependent industries: those that produce sheet mica, and those that produce flake mica. Each industry, although somewhat dependent on the other, produces different end products.
Sheet Mica Mining:
Sheet mica is recovered by either sinking a shaft along the strike and dip of a pegmatite or by open-pit surface mining of semi-hard pegmatite ore. In either case, it is a very economically risky mining procedure because of the cost involved in locating the vein and the unpredictability of the quality and quantity of the mica that might be recovered once the vein is located and worked.
In underground mining, the main shaft is driven through the pegmatite at suitable angles to the dip and strike using air drills, hoists and explosives. Crosscuts and raises are developed to follow promising exposures of mica. When a pocket of mica is found, extreme care is exercised in the removal to minimize damage to the crystals. Small explosive charges of 40% to 60% strength are carefully placed around the pocket and care is exercised with the drilling procedure so the mica will not be penetrated. The charge is just sufficient to shake the mica free from the host rock. After blasting, the mica is hand-picked and placed in boxes or bags for transporting to the
trimming shed where it is graded, split, and cut to various specified sizes for sale.
Sheet mica is no longer mined in the U.S. because of the high cost of mining, the small market, and the high capital risk. Most sheet mica is mined in India, where labor costs are comparatively low.
Flake Mica Mining:
The flake mica produced in the U.S. comes from several sources: the metamorphic rock called schist as a by-product of processing feldspar and kaolin resources, from placer deposits, and from pegmatites. It is mined by conventional open-pit methods. In soft residual material, dozers, shovels, scrapers and front-end loaders are used in the mining process. North Carolina's production accounts for half of total U.S. mica production. Hard-rock mining of mica-bearing ore requires drilling and blasting. After blasting, the ore is reduced in size with drop balls and loaded on the trucks with shovels for transport to the processing plant, where mica, quartz and feldspar are extracted.