Mica is an anhydrous silicate of calcium and aluminium, and crystallises in a laminated mass, easily split along its axis; it can be subdivided down to 3/1000, in thickness. Deposits of this material are found in various parts of the world. The occurrences of pockets in which mica is found cannot be predicted by the geological formation of the locality. The best quality mica is obtained from India, whence has been furnished the bulk of the world's supply for centuries. These mines, the principal of which is the Abruker mine, are in the interior of the country, remote from civilisation, and extremely inaccessible. Here the deposits are worked now as they were 2,000 years ago. The Abruker mine has been sunk about 200ft., following the pitch of the vein, and all the mica, and rein e are raised and carried a way by natives. No machinery of any kind is used; drills and hammers are the only to tools employed. The refuse and the mica are placed in baskets which each bold about 10 lb., and which are passed up from hand to hand by women who stand in a line on a ladder. When the top is reached the baskets are dumped and returned down the ladder- in the same manner, but by another line of women.

The crude mica, is first roughly trimmed and then sorted into different grades, according to sizes and qualities. It is then split up, and the size to which it is to be sheared is marked upon it. After shearing, the mica, is cleaned, weighed, and packed ready for transport.At the Abruker mine the packages of mica are loaded into carts drawn by bullocks, and carried in this way to seaports hundreds of miles away; the bullocks travel at the rate of about ten miles a day. There are many kinds of mica, prominent among which are Muscovite, the common potash mica: paragonite, an analogous soda variety; biotite, a magnesia mica having a black or dark green colour; phlogopite, a bronze-coloured mica found in crystalline limestone and serpentine rocks; lepidome-laue, a black mica containing much iron; and lepidolite, the red-rose or lilac lithia mica. Mica has many uses, its chief perhaps being in the electrical industry. The fact that mica is elastic and fireproof, and that its insuiating qualities are unaffected by time, has made it peculiarly adapted for use with electrical machinery. It has been used for vibrating plates in the photophone, and for diaphragms in telephone construction.

In commutator work mica is almost indispensable, as also is the case in hundreds of other electrical machines and instruments. For the purpose of armature insulation in high-tension alternating machines mica is especially adapted: unfortunately the expense of the mineral has to a great extent prohibited its use. Mica waste has one or two electrical uses. Insulators are made by splitting up the mica into lamina and solidifying these thin sheets at a high temperature and under a heavy pressure. It is claimed that this treatment increases the insulating properties of the mica. Mica replaces glass in positions exposed to much heat, is used in wallpaper varnish, and in packings for machinery: it has many other applications.