The Bridgeport times and evening farmer., 1922-06-29
Manufacturers Operate Own
 Mica Mines

Washington. June 29-Mica. that odd, heat-resisting. transparent m1n- eral which did duty as windows in the heating stoves of other days, has now become so essential in the cleo trical industry that the big electrical
 manufacturers own and operate their own mines, according to officials or the Bureau of Mines.
 Mica, they point out. includes group of several minerals characteriz- ed by a perfect basal cleavage, by virtue of which they may be split
 into exceedingly thin plates. The
 minerals are of very common oc- currence in all countries, constituting about 4 per cent. of the igneous rocks of the world. The term 'tisinglass'' is sometimes applied to glazing mica say this is incorrect, for true isin- glass is a soluble combustible mater iaI made from the air bladders of certain fish.
 Mistaken for Precious Metals
 "Silvery flakes of white mica and yellow flakes of altered black mica are commonly found in rocks and are
 often mistaken for the precious perts. "Any observeer," he continu-
 ed. may easily distinguish mica from gold or silver by testing with the
 blade of a sharp penknife. The mica
 will spit off in thin. flexible flakes and pu1verize to powdeer, while gold
 or silver have no cleavage and are malleable. The mica found as scat
 tered flakes in various types of rock
 is of no commercial value. Musco-
 Vite and phlogopite are only varieties that are of importance commercially"
 Mica possesses a combination of
 special qualities, the chief of which
 are elasticity. toughness, fexibility. transparency, ability to withstand ex-
 cessive heat and sudden changes in
 mperature. high dielectric strength.
 cleavability into thin films. and re-
 SiS Sfa tO darn1n noSiti0n substance possesses this combination of qualities. consequently no satfs-
 factory substitutes for mica are known for the more important uses. Valuable as Decorative.
 The brilIancy of the refiecting sur faces give mica special value for l decorative purposes. Muscovite in
 commercial sizes occurs in many parts of the world. Mica is found in masses known as books" varying in width and length from few inches
 to several feet, and in thickness from a fraction of an inch to six inches or more. Rum, ruby or green shades of color are most demand.
 In a recent year Canada, the United
 States and India produced about 97 per cent. of the world output of sheet mica. Of this amount India produces about 65 per cent. and the United States 5 per cent The output Of tirely mNscovite. whereas the Cana dian production is almost entirely phlogopite. The pre-war yearly world consumption of sheet mica was
 estimated at $500 short tons. Of this the United States consumed approxi- mately 49 per cent.
 In 1921 the mica producing states in order of production were as fol- lows: North Carolina. New Hamp- shire, Virginia, New Mexico, Georgia, South Dakota. California and Wiscon- sin. It's ability to withstand heat and its high electrical resistance has led to a wide application of sheet mica in the electrical industries.
 Used to InterIeave Segments. An important use of electrical mica is for interleaving between the copper segments of commutators. Thin films are used in vast numbers in cond ensers for magnetos and wireless apparatus. As sheets in greatly di- versified shapes. or as washers and tubes mica is used extensively as an insular in dynamos and in various fittings or appliances, in fuse boxes. sockets, insulators. electric heaters. fatirons and telep.lones. As a heat resisting transparent medium sheet mica has various uses. It was for merly widely employed for stove | windows. but this use has declined to l a considerable extent. Mica is also used in furnace sight-holes, heat
 screens, lamp chimneys, canopies and shades, particularly for gas mantles, also for military lanterns and in lam teren slides.