National Geographic : 1944 Jan
The National Geographic Magazine sages can be sent over a single transocean cable or long-distance wire at one time. Production of rock crystal in Brazil before the war was comparatively casual. Free-lance diggers furnished much of the output. Mines were mostly open cuts, worked largely in the dry seasons when water would not fill the pits. Japan and Germany were the principal buyers. Mineral that was of no value for scientific use was cut into necklaces and other decorative objects. Chief producing areas for quartz are the States of Minas Gerais and to a less extent Goiaz, Baia, and Mato Grosso. Many of the old mines are being re-explored and opened for production to meet expanded war demands. Ever larger quantities are being rushed to Allied war factories. Digging Crystals in Minas Gerais I visited several of the Minas Gerais mines, located about 75 miles northwest of the mod ern capital of Belo Horizonte. In one, near Sete Lagoas, some 500 men were digging in a yawning trench carved into the reddish-yellow earth. The scene looked like some building project conceived by the prehistoric cliff dwellers of our United States Southwest (Plates VII, VIII). The walls of the huge cut were stairstepped with big earth benches. For every man dig ging in the crystal-bearing vein in the bottom of the mine, six or eight others stood on the benches to throw out the waste material where it could be hauled away by mule carts and trucks. At a similar site some miles away I saw a snorting bulldozer at work. American ad visory engineers were supervising its opera tion. The machine had been shipped more than 400 miles by rail from Rio and then driven through bush and creeks to the mine. Earlier workers had literally dug themselves into a hole. They had quit mining when they had no more room for piling the waste. The bulldozer was ripping the earth overburden away from the rich workable vein and pushing it into the valley below, accomplishing more in a day than hundreds of men could have done in weeks by hand. Chemically, quartz is the same as sand. It is silicon dioxide, the most common of all solid minerals. To find crystals of suitable size and purity for technical use, however, is another story. The crystals vary in size from tiny hexag onal slivers, often clustered together, to huge six-sided blocks of rock. One crystal on dis play in Belo Horizonte weighs more than five tons! Some crystals are stained; others have frac tures, ghosts, cloudiness, or other defects. Even one which appears perfect to the eye may show flaws under polarized light (p. 77). In Rio the United States Office of Economic Warfare now operates cleaning and testing laboratories. In them later I watched dozens of men and girls chipping off defective por tions of larger crystals and testing each selected piece of quartz under the searching rays of arc lamps and polarized light before it was approved for shipment. A Miracle Mineral Is Mica Mica, like quartz, also has heavy wartime demand. A remarkable mineral this. It is so formed and crystallized in nature that it can be readily separated into thin flexible sheets. "Isinglass" is the popular term for the trans parent pieces of mica used as windows in coal stoves and in electric ranges. It appears in your prewar toaster, electric iron, radio tubes, condensers, and other gadgets. Pow dered mica was your Christmas tree "snow." Its electrical-insulation and heat-resistant qualities, plus its transparency, flexibility, and the thinness to which it can be split have given this mineral an amazing number of uses. In normal years Brazil was the world's fifth largest producer and exporter of mica. Al though the United States produces quantities, British India has long held the lead for mus covite mica. Madagascar held a similar domi nant position for the amber mineral. Of late, even before the war raised it to priority status, Brazilian mica was coming more and more into use. It is so common in some parts of the coun try that flecks glitter in the roads. In Minas Gerais alone 20 districts have been exploited. The State of Rio de Janeiro and other locali ties also have considerable deposits. "Books" of mica being uncovered in the pegmatite dikes of the mica schist areas in eastern Minas Gerais varied in size up to one and one-half feet square and several inches in thickness (page 43). The pieces of so-called "mica bruto," or crude mica, after being removed from the mines are first split into sheets to the thick ness of light cardboard and trimmed of their irregular edges. Much is sent from the mines in this form. In interior towns and in Rio I saw many mica-trimming shops where girls deftly split the thick sheets into thinner layers, cut off stains and imperfections, and sometimes to the untrained eye slashed a big sheet into a pitifully small square (page 76).