Found in pegmatite granite dikes. It is stated to be inferior to amber mica phlogopite for electric motor and dynamo manufacture, as it wears faster and is somewhat brittle. India is the largest producer, though Quebec, Ontario, and British Columbia, and other countries produce muscovite. Value, as quoted in market reports, according to size, quality, and color. A rare rock occurs that consists entirely of biotite. By the rules of nomenclature it is called biotite, but it also has the fine name glimmerite.
Celadonite is best known in the geologic setting shown here: filling openings vesicles in basaltic lava, whereas glauconite forms in sediments of the shallow sea. It has a bit more iron Fe than glauconite, and its molecular structure is better organized, making a difference in x-ray studies. Its streak tends to be a more bluish green than that of glauconite. Mineralogists consider it part of a series with muscovite , the blend between them being called phengite. Celadonite is well known to artists as a natural pigment, "green earth," that ranges from bluish green to olive.
It is found in ancient wall paintings and is produced today from many different localities, each with its particular color. Its name means "sea-green" in French. This specimen is from the Minas Gerais province of Brazil.
It forms by alteration of other micas in marine sedimentary rocks and is used by organic gardeners as a slow-release potassium fertilizer.
It's very similar to celadonite , which develops in different settings. This lepidolite specimen consists of tiny lepidolite flakes and a quartz matrix whose neutral color does not obscure the characteristic color of the mica. Lepidolite can also be pink, yellow or gray. One notable occurrence of lepidolite is in greisens, bodies of granite that are altered by fluorine-bearing vapors. That's what this may be, but it came from a rock shop with no data on its origin.
Where it occurs in larger lumps in pegmatite bodies, lepidolite is an ore of lithium, especially in combination with the pyroxene mineral spodumene, the other relatively common lithium mineral. It is pale pink, green or yellow and is not as flexible as other micas.
Muscovite, KAl 2 Si 3 AlO 10 OH,F 2 , is a high-aluminum mica common in felsic rocks and in metamorphic rocks of the pelitic series, derived from clay. Muscovite was once commonly used for windows, and the productive Russian mica mines gave muscovite its name it was once widely known as "Muscovy glass". Today mica windows are still used in cast-iron stoves, but the greater use of muscovite is as insulators in electrical equipment.
The mineral has been known for millennia: Mica was first mined in India about 4, years ago, where it was used primarily in medicines. The Mayans used it for decorative effect in stucco to make their temples sparkle in the sun. Today it is used in everything from electrical products to makeup. Mica is highly reflective, and its excellent cleavage allows it to split into thin sheets; these tough, flexible sheets are the distinguishing characteristic of the mineral group.
Thin sheets are transparent or, if deeply colored, translucent. Micas are stable when exposed to electricity, light, moisture and extreme temperatures.
Commercial forms of mica can be grouped as either unmanufactured or manufactured. Unmanufactured mica can be divided into two classes: sheet mica and scrap mica, which includes flake mica. Most sheet mica is mined in India, where labor costs are comparatively low. The flake mica produced in the U. 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. 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.
The principal use of ground mica is in gypsum wallboard joint compound, where it acts as a filler and extender, provides a smoother consistency, improves workability, and prevents cracking.
In the paint industry, ground mica is used as a pigment extender that also facilitates suspension due to its light weight and platy morphology.
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