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 States (South Dakota, Colorado and Alabama), and Brazil (Goyaz, Bahia and Minas Geraes). The commercially valuable micas of Canada and Ceylon are mainly (q.v.), which has a rather different mode of occurrence. The mica mined in India is practically all Muscovite. The principal mining districts are those of Hazaribagh in Bengal and Nellore in Madras; in the former district the mica has usually a ruby tint, whilst in the latter it is more often greenish. In the Inikurti mine, Nellore, “books” of mica measuring 10 ft. across, and up to 15 ft. across the folia have been found, and rectangular sheets measuring 30 by 24 in. and free from cracks and flaws have frequently been obtained.

Uses.—On account of its transparency and its resistance to fire and sudden changes of temperature, mica has been much used for the windows of stoves and lanterns, for the peep-holes of furnaces, and the chimneys of lamps and gas-burners. At one time it was used for window panes of houses and the port-holes of Russian men-of-war, being commonly known as “Muscovy glass.” Spangles of mica are much used for decorative purposes of various kinds, and the mineral was formerly known as glacies Mariae (Ger., Frauenglas) because of its use for decorating statues of the Virgin. The lapis specularis of Pliny, scattered over the Circus Maximus to produce a shining whiteness, was probably mica. 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. Sheets of mica are used as a surface for painting, especially in India; for lantern slides; for carrying photographic films; as a protective covering for pictures and historical documents; for mounting soft and collapsible natural history specimens preserved in spirit; for the vanes of anemometers; mirrors of delicate physical instruments; for various optical and many other purposes. Being a bad conductor of heat it is used for the packing and jackets of boilers and steam-pipes. Other applications depend on the strength of its resistance to acids.

The most extensive application of mica at the present day is for electrical purposes. Being a bad conductor of electricity it is of value as an insulator, and the smooth flexible sheets are much used in the construction of armatures of dynamos and in other electrical machinery. For various purposes a manufactured material known as “micanite” or “micanite cloth” is much used; this consists of small sheets of mica cemented with shellac or other insulating cement on cloth or paper.

Muscovite and phlogopite are practically the only species used commercially, the former being the more common. Phlogopite is rarely found as colourless transparent sheets and is therefore almost exclusively used for electrical purposes. Many other uses of mica might be mentioned. The potassium it contains renders it of value as a manure. The species lepidolite is largely used for the manufacture of lithium and rubidium salts.

Mining, Preparation and Value.—Mica mining is an industry of considerable importance, especially in India; but here the methods of mining are very primitive and wasteful. In working downwards in open quarries and in tortuous shafts and passages much of the mica is damaged, and a large amount of labour is expended in hauling waste material to the surface. Since the mineral occurs in definite veins, a more satisfactory and economical method of working would be that adopted in metalliferous mines, with a vertical shaft, cross-cuts, and levels running along the strike of the vein: the mica could then be extracted by overhead stopping, and the waste material used for filling up the worked-out excavations.

In dressing mica the “books” are split along the cleavage into sheets of the required thickness, and the sheets trimmed into rectangles with a sharp knife, shears or guillotine, stained and damaged portions being rejected. The dressed sheets are sorted according to size, transparency, colour and freedom from spots or stains. Scrap mica is ground to powder or used in the manufacture of micanite.

The price of mica varies very considerably according to the size, transparency and quality of the sheets. An average price for cut sheets of all sizes is about 4s. per ℔, but for large sheets it may be as high as 54s. per ℔.

.—For the mineralogical characters see the textbooks of J. D. Dana and C. Hintze; for economic questions, the following: T. H. Holland, “The Mica Deposits of India,” Memoirs of the Geological Survey of India (1902), xxxiv. 11–121; G. P. Merrill, The Non-Metallic Minerals (New York, 1904), pp. 163–180; “The Mining and Preparation of Mica for Commercial Purposes,” Bulletin of the Imperial Institute (London, 1904), ii. 278–291; F. Cirkel, “Mica: its Occurrence, Exploitation and Uses” (Canadian Dept. of the Interior, Mines Branch, Ottawa 1905, 148 pp.).

 MICAH, in the Bible, the name prefixed to the sixth in order of the books of the minor prophets. He was a contemporary and fellow-worker of Isaiah. The name in various modifications—Mīcāiāhū, Mīcāiĕhū, Mīcāiāh—is common in the Old Testament, expressing as it does a fundamental point of Hebrew faith: Who is like Yahweh? It was also borne among others by the Danite whose history is given in judges xvii. seq. (see separate article), by the prophet who opposed Ahab’s expedition to Ramoth-Gilead (1 Kings xxii.), and by the son of Jonathan (see ).,

The editorial title of the book of Micah declares that Micah prophesied “in the days of Jotham (739–734), Ahaz (753–721) and Hezekiah (720–693), kings of Judah.” Nothing in the book itself can claim to belong to the reign of Jotham, but the prophecy against Samaria (i. 5–8) may have been uttered originally before the fall of Samaria in 722, i.e. in the reign of Ahaz. In its present form, however, it has been incorporated in a prophecy against Judah, belonging, most probably, to the years 705–701, when a new Palestinian rising provoked Sennacherib’s campaign of 701 (Nowack; cf. Marti). This prophetic activity of Micah under Hezekiah is confirmed by the direct statement of Jer. xxvi. 17 seq., where Mic. iii. 12 is quoted (“Zion shall be plowed as a field,” &c.). The verse quoted forms the climax of Mic. i.–iii., from which chapters only any certain conclusions as to the prophetic message of the historic Micah can be drawn; the remaining sections of the present book (iv.–v., vi.–vii.) consist, in whole or in greater part, of writings belonging to a later period.

Chs. i.–iii. (with the exception of two verses, ii. 12, 13) are a prediction of judgment on the sins of Judah and Ephraim. In a majestic exordium Yahweh Himself is represented as coming forth in the thunderstorm (cf. Amos i. 2) from His heavenly palace, and descending on the mountains of Palestine, at once as witness against His people, and the executer of judgment on their sins. Samaria is sentenced to destruction for idolatry; and the blow extends to judah also, which participates in the same guilt (ch. i.). But, while Samaria is summarily dismissed, the sin of Judah is analysed at length in chs. ii. and iii., in which the prophet