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MICA

The name mica was derived from the Latin micare which meant to shine. The name Muscovite was derived from the term muscovy-glass which it was previously known by because of its widespread use as a glass substitute in the Old Russian state of Muscovy in the 14th century. The micas are complex hydrous potassium-aluminum silicate minerals. There are more than 20 chemically distinct mica species with considerable variance in geologic occurrence, but all have essentially the same crystal structure. The micas crystallize with a sheet structure, the sheets being held together by relatively weak bonds resulting in the perfect basal cleavage of the micas. In Latin Mica means “To Shine” or to “Glitter”.

TYPES OF M ICA

a) MUSCOVITE (Potassium Mica) “H2KAl3(SiO4)3
Muscovite is the pure potassium mica, containing no impurities. Muscovite mica also is a very widespread and common rock forming mineral. In igneous rocks it has the characteristic of granites and granite pegmatites, and in metamorphic rocks it is very common. In some mica schists and quartzites, muscovite crystallizes with chromium impurities resulting in the emerald green colored variety fuchsite.

b) BIOTITE (Magnesium Iron Mica) “(H2K)(Mg, Fe)3Al(SiO4)3
Biotite is the most common of the micas, containing iron and/or magnesium impurities substituting for octahedral aluminum. Biotite mica
is the most common of the micas; in fact it is the most common ferromagnesian mineral. It occurs in most igneous and metamorphic rocks.

PHYSICAL PROPERTIES:

i. CLASS: Phylosilicate

ii. CRYSTAL SYSTEM: Monoclinic

iii. SPECIFIC GRAVITY: 2.2 – 3.3

iv. HARDNESS: 2.0 – 4.0

v. LUSTER: Viterous, pearly, metallic

vi. CLEAVAGE: Perfect basal cleavage

vii. STREAK: White

viii. COLOR: Dark Green, White, Grayish White

Uses:
Mica is used in drilling fluids to prevent loss of circulation and as a sealant. Mica is a good sealant because the sheet particles overlap each other sticking to the side of hole and creating a sealed wall. This helps to keep circulation in the hole. Mica and bentonite are commonly used together in drilling fluids. They both help to seal zones; however mica's main purpose is to prevent loss of circulation. Muscovite (white) mica is used in electronic insulators; ground mica in paints, as joint cement, as a dusting agent, in well-drilling mud and lubricants; and in plastics, roofing, rubber and welding rods.