The turquoise runs in blue veins through the rocks, with now and then the concretions called nuggets, which afford stones of value. At the present time the bulk of the world's supply of fine turquoise is drawn from New Mexico, and experts say that that the output is equal to the best turquoise from Persia. Indeed, it is in one respect superior, holding itscolor better. About $200,000 worth of turquoise are sold annually. For the first time in centuries it is possible, jewelers say, to make a turquoise necklace of perfectly matched stones. The turquoise occurs in a rock of a pretty reddish color, being so mixed up with it ordinarily as to be valueless. But the idea came to a gem expert in New York not long ago that it would be a good idea to take selected pieces of this stuff and polish them, offering them for sale under the name of matrix turquoise. To his own astonishment, the idea proved immensely popular; a fad for stones of this kind rapidly grew; and today, following out the-same idea, jewelers sell matrix sapphires, matrix emerals, and matrix rubies. In fact, almost any flawed gem, filled in with ordinary rock stuff and impossible for cutting, will bring a high price as genuine matrix.

That quartz is opaque is due largely to the myriad cavities which it contains. These cavities may be vacant, but often they contain water and liquified carbonic acid gas. Sorby discovered the fact that they may be so microscopic in size that a thousand millions of them in a cubic inch is not unusual, and the enclosed water often constitutes one to two per cent of the volume of the quartz.

In sandstone the grains of sand are rounded, having no sharp edges as in granite.

In the early days of tunneling, machine drills were mounted on cars running on tracks, and this is still the practice in some parts of Europe.

One of the causes of loss in the transmission of compressed air is pumping the air of the engine room rather than that drawn from a cooler place. The loss amounts to from 2 to 10 per cent.

In the middle ages the monks devoted themselves to alchemy, but, after failing repeatedly, were prohibited by the Pope from studying the art.

Mufflers to minimize the noise of the escape of exhaust steam from high-pressure steam engines are sometimes needed. A good muffler is made by inserting, near the engine, a chamber of 15 or 20 times the volume of the cylinder and continuing the exhaust pipe from this chamber. This will do away with the disturbance caused by steam passing through a tortuous exhaust pipe.