These thin laminae are easily cut with a pair of shears into any desired form, and are then ready for any further process necessary to fit them for the purpose for which they are intended.

The facility with which they can be bent into various shapes, and the power they possess of resisting heat, together with their transparency and naturally beautiful appearance, make these thin sheets of mica of peculiar value in many situations. They have been used as reflectors for some years, and a patent has recently been obtained in this country for an improved process of silvering plates of mica, the inventor being a resident of Philadelphia. The flexible nature of the material to be silvered will probably ensure its introduction into the arts and industries to a greater or lesser extent, and it is perhaps not impossible that it may be employed in the manufacture of telescopes, although it must be confessed that its utilization for that purpose is rather improbable. In the process recently patented, sheets of mica, as free from metallic deposit as can be obtained, are thoroughly washed in nitric acid, and then rinsed in water. They are then placed upright in suitable vats or baths, being arranged in pairs, back to back, so as to expose only one side to the coating solution. This latter is tolerably well known, and is made by dissolving 1 oz. nitrate of silver in 1 qt. distilled water, and in a separate vessel 1 oz. glucose in 1 qt. distilled water.

When the silver has dissolved, a small quantity of liquor ammonias is added, and the solution becomes cloudy, the cloudiness disappearing on the addition of a little more ammonia. When this stage has been arrived at, the 2 solutions are mixed together and poured into the bath containing the mica plates, the bath being placed in a warm room, to facilitate the deposition of the silver. When the mica plates are sufficiently coated, they are withdrawn from the bath, thoroughly rinsed in water, and stood away to dry, after which they may, if deemed necessary, be coated with spirit varnish.

The mica plates thus prepared may be mounted on frames of tin, sheet-iron, paper, or plastic composition. Many other applications of these mica reflectors will suggest themselves, though their principal use is undoubtedly for illuminating purposes. The inventor of the process claims the right of constructing reflectors and shades in the manner described, but, inasmuch as the method of silvering is certainly old, and reflectors made of mica have been known for years, we doubt whether he could succeed in upholding the validity of his patent. {Eng. Mech.)

In India, small fragments of mica are largely employed in the tinsel decoration of temples, palaces, banners, etc. In powder, it is used for ornamenting pottery, and even the clothes of the natives. By native artists it is much in vogue for painting on. Although mica is one of the most widely distributed minerals in India, its occurrence in plates of sufficient size to be of commercial value is limited to a few particular tracts. All the mica which-occurs in rocks other than those of crystalline or metamorphic character is fragmentary or detrital, and of no substantial value, though it is collected to a small extent by the natives for ornamental purposes. The plates of useful size are found generally in veins of coarsely crystalline granite.

In the year 1826, large transparent laminae were procured a few miles to the east of Hazaribagh station. In 1849, Dr. McClelland described the mica mines at Dhanwi, Dhoba = Dhunbhar (?) and Quadrumma. At Dhanwi the mica is said to occur in strata alternating with coarse gneiss. The plates are associated with large crystals of felspar and amorphous masses of quartz. About 50 to 100 men and boys were engaged in the mines, which were inclines running with the dip., and as many more women and children occupied themselves with sorting and dressing the plates.

At Dhub and at Jamtara, in the Kharakdiha pargana, are mica mines which have been described by Mallet as follows:-Having given the geological relations of the granite dykes, which he considers to be truly intrusive, he says that the coarsest pegmatite is frequently found in dykes of moderate thickness, in which therefore plates of the largest mica occur, and it is such dykes that the miners generally select for their operations. They pay 1 to 2 rupees each per annum, according to the richness of the yield, to the owner of the land for the privilege of mining. The usual mode of working is simply to excavate a trench along the course of the dyke, which In the Gawan neighbourhood is seldom carried deeper than 20 or 25 ft. Sometimes, where a considerable thickness of decomposed mica is near the surface, rude shafts are sunk to the fresh and uninjured mineral, and excavations are carried on laterally from the bottom. In a few cases also, rough horizontal galleries are driven in from the side of a hill. In the last methods, of course artificial light is necessary. No precautions are taken to support the roof, and accidents are not unfrequent from its falling in.

The-plates of mica are generally brought to the miners' villages, and there, after being slightly trimmed with ordinary grass-cutting knives, they are sorted into different heaps according to quality and size. The quality depends on the mineral being in a perfectly unaltered condition, on its transparency and freedom from cloudiness caused by internal foreign matter, on the absence of minor cleavages which render it liable to split into ribbons and triangles, and on the planeness of its fissile surfaces. Six kinds are recognised, according to the size of the plates, viz. (1) sanjhla; (2) manjhla; (3) rasi; (4) karra; (5) urtha; (6) admalla. Some of the miners interpolate failurtha between the fifth and sixth, and speak of another size, barha, still larger than admalla. All these terms are used rather vaguely in respect to the absolute size of the plates indicated thereby. At Dhub and Jamtara the miners were induced to separate a quantity of the mica into the different grades; measured average specimens of each gave the following results:-

The above 4 sizes include the greater portion of the mica found, it being only in the best mines that urtha and admalla are procurable. The largest plates which were seen measured 19 x 14 in., and 20 X 17 in., but considerably larger ones are sometimes obtained. The mica la sold by the load, which is built up of ■ plates, either into one frustum of a cone, and carried on the head after being bound together with a cord, or in two such, and carried in a banghi A load equals 6 panseries, one panseri being equal to 5 kachcha seers of 12 chittacks each, or 3 3/4 pakka seers of 16 chittacks; the load, therefore, being 22 1/2 seers, or 46 lb. avoirdupois. The miners stated that the prices paid to them per load by the mahajans were as follows: sanjhla, 3 annas; manjhla, 5 annas; rasi, 7 annas; karra, 12 annas; urtha, rs. 2 to rs. 5; admalla, rs. 4 to rs. 9; the selling prices being about double these figures. The value of the large plates more especially varies greatly with the quality. According to Colonel Boddam, plates of first quality of 18 in; diameter fetch as much as rs. 60 a mound in the market, or about rs. 30 a load.

Within the past few years some attempts have been made by a European to work some of these mines, but with extension of the operations the trouble and expense caused by water have increased so much that the work has, it is believed, been abandoned. (Ball, Economic Geology of India,) ____ ____