Quartz crystals are urgently needed in large quantities for making quartz crystal oscillator plates used in radio equipment for the armed forces. At present all of the quartz used for this purpose comes from Brazil. This supply is not sufficient, however, and it is necessary to find and develop further sources in the United States.
There is no difficulty in finding low grade quartz.
Quartz is perhaps the world's commonest mineral.
It is found abundantly as boulders and pebbles or as veins and grains in granite and other rocks.
But the large clear quartz crystals required for radio purposes are not common at all, though they do occur in some places lining cavities in rock, and in the dirt and gravel nearby.
Only separate, individual crystals are wanted-not groups or clusters or grainy masses. Each separate crystal must weigh at least one-half pound. Measured in inches, the crystals must be at least an inch thick and three inches long. Crystals with natural faces are preferred but crystals with all the faces broken off can still be used. The above sizes are the-smallest that can be used. Larger sizes, between one and four pounds, are preferred.
Each crystal must be clear and colorless on the inside. Clear means clear as glass, perfectly clear and transparent, so that a newspaper can be read through the crystal.
It is not necessary that the whole crystal be perfect, but large portions of the crystal must be perfect, and these are the parts which are cut out and used. These parts must be entirely free from specks, bubbles, and lines on the inside, absolutely free from clouds, cracks and flaws of any kind. These parts must be at least as large as walnuts.
Furthermore the bad portion of the crystal must not be more than twice the volume of the perfect portions.
The reason for this is that it would not pay to do too much sawing in order to cut away the bad part of the crystal from the perfect part. Quartz crystals are often good near the pointed end but bad at the base end. In this case the bad end can usually be knocked off carefully with a hammer so that the remaining crystal is mostly good. Some crystals which appear to be perfect are useless because of the optical twinning, but this is determined only with special equipment.
Colored quartz is not wanted. Milky quartz, purple quartz (amethyst), rose quartz cannot be used. The only exception is that light smoky quartz can be used, otherwise quartz must be colorless.
The outside of the crystal does not matter except that it is necessary to look through the crystal in order to see flaws on the inside. Some quartz crystals are covered with iron stain but this can be removed and does no harm.
Anyone who owns or knows of a location where such material can be produced in quantity is requested to send a sample consisting of several of the best crystals he can select to the Miscellaneous Minerals Division, War Production Board, Temporary "R" Building, Washington, D. C. R. H. 0.