14 MINERAL, RESOURCES, 1918----PART II.
Fluorite
suitable for optical use is valued at from $1 to $10 a pound, according
to the size of the piece suitable for cutting as well as to its
quality. The present yearly requirement is not large—perhaps several
hundred pounds—but under proper conditions and with a dependable steady
supply this requirement may be increased.
Possible
buyers of optical fluorite are: Bausch & Lomb Optical Co.,
Rochester, N.Y.; Spencer Lens Co., Buffalo, N. Y.; Ward's Natural
Science Establishment, Rochester, N. Y.; United States Bureau of
Standards, Washington, D. C.
Suitable
material has been obtained from several of the fluorite mines in Hardin
County, 111., and may also occur in the extension of this fluorite belt
in western Kentucky. Although fluorite is found in many other States,
practically none of them is known to contain any "optical fluorite."
Among publications dealing with optical fluorite are the following:
Pogue, J. E., Optical fluorite in southern Illinois: Separate from Bull. 38, Illinois State Geol. Survey, Urbana, 111., 1918.
Burchard, E. F., Fluorspar and cryolite in 1917: U. S. Geol. Survey, Mineral Resources, 1918, pt. 2, pp. 301-302, 1918.
U. S. Bureau of Standards, Washington, D. O: Circular letter dated May 8,1918. Quartz. See Rock crystal.
Rock crystal.—The
perfectly clear and colorless variety of quartz is called rock crystal.
It furnishes the material for certain special glasses and fused silica
ware; and it is used in wedges for microscopic work, as spectographic
prisms for special researches, and as mechanical bearings. A use in
connection with certain sounding boxes has recently been developed. Sepiolite. See Meerschaum.
Sapphire. The
variety of gem corundum used for other purposes than jewelry is called
sapphire, irrespective of its color. It is used for mechanical bearings
and pivot supports, especially in watches and phonograph needles
(mostly artificial sapphire). Topaz. Abrasive.
Tourmaline. In the tourmaline tongs or in polarizing forceps, a very simple form of polariscope.
