noun
definition
Any of a group of hydrous aluminosilicate minerals characterized by highly perfect cleavage, so that they readily separate into very thin leaves, more or less elastic.
Examples of mica in a Sentence
The mica mined in India is practically all muscovite.
Mica is mined near Mrogoro.
In 1870 North Carolina's mica mines were reopened, and they produce the best grade of sheet mica for glazing and a large percentage of the country's yield of this mineral.
Inclusions of other minerals are frequently to be observed in mica.
For the more delicate species, such as the Callithamnia and Ectocarpi, it is an excellent plan to place a small fruiting fragment, carefully floated out in water, on a slip of mica of the size of an ordinary microscopical slide, and allow it to dry.
The most extensive application of mica at the present day is for electrical purposes.
Large quantities of ground mica are used in the manufacture of wall-paper, and to produce a frosted effect on toys, stage scenery, &c. Powdered mica is also used in the manufacture of paints and paper, as a lubricant, and as an absorbent of nitro-glycerine and disinfectants.
Most of the island is occupied by the band of the old rocks, which include mica, glaucophane and sericite-schists and slates; there are small intrusions of granite, and numerous dikes and masses of basic eruptive rocks.
Within these limits are to be found most of the minerals known - gold, silver, quicksilver, copper, lead, zinc, iron, manganese, wolfram, bismuth, thorium, vanadium; mica, coal, &c. On or near the coast are coal, salt, sulphur, borax, nitrates and petroleum.
Quincy granite takes a very high polish, owing to the absence of mica and to the coarser cleavage of its hornblende and augite.
Silver follows gold in importance, but the other minerals met with, including gypsum, mica, petroleum, natural gas, granite, marble and tin are not found in paying quantities.
Slates consist largely of thin plates of mica arranged parallel to the cleavage faces.
This mica has developed in the rock as it was folded and compressed.
The faces of slates have usually a slightly silky lustre due to the abundance of minute scales of mica all lying parallel and reflecting light simultaneously from their pearly basal planes.
In microscopic section the best slates show much colourless mica in small, thin, irregular scales.
The spots contain variety of minerals, sometimes mainly white mica or chlorite.
In point of absolute mass they are insignificant compared with the abundance and variety of potassiferous silicates, which occur everywhere in the earth's crust; orthoclase (potash felspar) and potash mica may be quoted as prominent examples.
These crystals may be half an inch to several inches in length; they are usually more or less completely weathered to white mica and kaolin.
The card or "fly," formerly made of cardboard, now consists of a disk either of mica covered with paper or of paper alone, but in all cases the card is divided into points and degrees as shown in fig.
The mica card is generally mounted on a brass framework, F F, with a brass cap, C, fitted with a sapphire centre and carrying four magnetized needles, N, N, N, N, as in fig.
The card is a mica disk, either painted as in fig.
Beneath there appears to be an unbroken surface of mica schist.
The water which has found its way through the granitic sand flows over the surface of the mica schist and settles in the hollows, and by sinking wells to the solid rock a supply of water can generally be obtained.
The other minerals found in the concentrates are pebbles and fragments of pyrope, zircon, cyanite, chrome-diopside, enstatite, a green pyroxene, mica, ilmenite, magnetite, chromite, hornblende, olivine, barytes, calcite and pyrites.
From these rocks in the Ottawa valley are quarried or mined granite, marble, magnificent blue sodalite, felspar, talc, actinolite, mica, apatite, graphite and corundum; the latter mineral, which occurs on a larger scale here than elsewhere, is rapidly replacing emery as an abrasive.
The soil of the Delta is a dark grey fine sandy soil, becoming at times almost a stiff clay by reason of the fineness of its particles, which consist almost wholly of extremely small grains of quartz with a few other minerals, and often numerous flakes of mica.
The Eastern Cordillera is composed of gneiss, mica and chlorite schist and other crystalline rocks of ancient date; the Western Cordillera, on the other hand, is formed of porphyritic eruptive rocks of Mesozoic age, together with sedimentary deposits containing Cretaceous fossils.
Putting aside salt, which has been already treated, the chief mining resources of India at the present day are the coal mines, the gold mines, the petroleum oil-fields, the ruby mines, manganese deposits, mica mines in Bengal, and the tin ores and jade of Burma.
Mica has long been obtained in Bengal, chiefly in the Hazaribagh district, and there is a rubycoloured variety which is held in great estimation.
In Madras also a mica industry has recently grown up. Tin is found in the Tavoy and Mergui districts of Lower Burma, and has for many years been worked in an unprogressive manner chiefly by Chinese labour.
In other cases, Leyden jars or condensers take the form of sheets of mica or micanite or ebonite partly coated with tin foil or silver leaf on both sides; or a pile of sheets of alternate tin foil and mica may be built up, the tin foil sheets having lugs projecting out first on one side and then on the other.
All the lugs on one side are connected together, and so also are all the lugs on the other side, and the two sets of tin foils separated by sheets of mica constitute the two metallic surfaces of the Leyden jar condenser.
It is found in the minerals lepidolite, petalite and in various specimens of mica and of carnallite, and in some mineral waters.
Iron ores are widely distributed, but have not been developed; graphite is mined in Colfax county; mica in Taos county, and to a small extent in Rio Arriba county; marble is quarried in Otero county and sandstone in Bernalillo, Colfax and San Miguel counties.
The rock is a very compact and fine-grained mixture of felspar, quartz and mica, often graduating to mica schist, quartzite and gneiss.
In the western and northern alpine part of Sweden, near the boundaries of Norway, the Silurian strata are covered by crystalline rocks, mica schists, quartzites, &c., of an enormous thickness, which have been brought into their present positions upon a thrust-plane.
In the upper chamber, about half-way between the centre of the base and the apex, was a single skeleton, adorned with beads, copper bracelets and plates of mica; in the lower chamber, directly under the upper and partly in the natural earth, were two skeletons, one adorned with beads and the other without ornament.
The primary rocks which appear at Mitushev Kamen are overlaid with thick beds of quartzites and clayslates containing sulphide of iron, with subordinate layers of talc or mica slate, and thinner beds of fossiliferous limestone, Silurian or Devonian.
The Russian Altai is composed mainly of mica and chlorite schists and slates, together with beds of limestone, and in the higher horizons Devonian and Carboniferous fossils occur in many places.
Mica schists form the prevalent rocks.
It is only found in combination, and is a constituent of the minerals petalite, triphyline, spodumene and lepidolite or lithia mica.
Quincy granite, a hornblende, pyroxene, bluish or greyish, without mica, was used for the construction of the Bunker Hill monument at Charlestown (in 1826), and of King's Chapel, Boston; and for interior decorations it has found some use, for example in the Philadelphia city buildings.
Geologically, the Erzgebirge range consists mainly of gneiss, mica and phyllite.
Among other manufactures are hosiery and knit goods, overalls and suspenders, hardware, lumber, oils and varnishes, gasoline fire engines, mica insulators, agricultural implements, and wagons and carriages.
The gneiss is mostly grey, but occasionally pinkish, its essential constituents (felspar and quartz) being almost always associated with dark mica (biotite) and hornblende in variable quantity.
Such plates are generally made of mica or selenite, and the normal to the plane of polarization of the most retarded stream is called "the axis of the plate."
Below the analyser G a plate H of selenite or mica may be put in the course of the rays.
Some of these are recognizable as pale yellowish and white mica; others seem to be chlorite, the remainder is perhaps kaolin, but, owing to the minute size of the flakes, they yield very indistinct reactions to polarized light.
It consists of very fine scaly kaolin, larger, shining plates of white mica, grains of quartz and particles of semi-decomposed felspar, tourmaline, zircon and other minerals, which originally formed part of the granite.
The felspar decomposes into kaolin and quartz; its alkalis are for the most part set free and removed in solution, but are partly retained in the white mica which is constantly found in crude china-clays.