MICA.
Kobub-ul-arz, . ARAB. Glimmer, DA., DUT., GER. Kin-sing-shill, . Citt N. Tulk, . . 1) ux., PERS.
Yin-sing-ahih, . „ Abraka, . . . SANSK.
Mica is one of the constituents of granite, gneiss, and mica-slate, and gives to the latter its laminated structure. It also occurs in granular limestone. It is found abundantly in India and other parts of the world. The principal mica mines of Behar are on the northern face of the Vindhya Hills, where the three districts of Behar, Monghir, and Ramgarh meet. The most westerly mine is situated 37 miles in a S.E. direction from Gya, and is in the district of Behar ; the most easterly mine is about 60 miles distant in Zillah Monghir, the whole of the intermediate 60 miles being more or less productive of the mineral. The mica reaches the surface in three different states, viz. the good, hard, and serviceable mineral ; the soft, wet, and flimsy mineral; and the chipped and powdered mineral. The tests as to whether the mica is good for anything, or whether, as the natives say, 'it is alive,' are its firmness, specific gravity, and the power of re flecting the countenance free of contortions ; the latter test showing the perfect parallelism of its individual plates, and consequent likelihood to split well ; the heavier the mineral and the more perfect the reflection, the more valuable is the mineral considered ; all the plates not standing the necessary test, or of a soft and flimsy nature without any of the brilliant sparkle of the better sort, the natives call 'dead mica,' and it appears to be in a state of decay. The plates of the superior kind are used in all the large Gangetic cities and towns by the native draftsmen, whose beautiful productions in body colours must be familiar to most people ; by the lamp and toy-makers ; by the Muhammadans for ornamenting their tazia or tabut, as well as for ornamenting umbrellas and boats, and for making artificial flowers. The second and third sorts aro pounded and used for ornamenting toys, pottery, the inside of houses, for sprinkling over clothes and turbands at feasts, the sparkle from which by torch-light resembles diamonds ; but the great consumption of the in ferior mineral takes place during the Iloli festival, during which period the abir of pounded mica, mixed with the flour of the small grain Kodu, Paspalum stoloniferum, Linn., and coloured with
some red-colouring matter, is freely sprinkled over the votaries of those bacchanalian orgies. Mica is the soft shining scaly part of granite, and is very liable to decay from constant damp ; it passes into a greasy or soapy earth or loam. Mica is mixed with lime to form a beautiful glistening plaster for native buildings.
In Russia it is used as a substitute for glass, and hence it is called Muscovy glass. The very thin laminae are employed for examining objects under the microscope. Slips of mica afford a convenient substitute for platinum foil in chemical experiments on the effect of heat on organic bodies, and they are useful for covering photo graphs. It readily splits into transparent, elastic flakes. It consists of nearly equal parts of silica and magnesia, and about 6 per 100 of lime. Mica has been used as a substitute for glass ; in the taking of collodion pictures, the collodion film adheres to it very firmly. On it negatives can be as easily carried, without injury, in a portfolio, as on paper, and positives backed with colour and a plain varnish can be pasted, without risk of deterioration, in a book. The mica being attached to a piece of glass by its back being moistened, may be then coated, exposed, and developed, after which it may be detached and fixed. Upwards of 1000 maunds, or nearly 40 tons, are sent to Calcutta annually, of the value of Rs. 7500 at Rs. 7i per maund.—Capt. Sherwin, Beng. As. Soc. Jour.,1851; Cat. Er., 186Z; 0' Shaughnessy.