The peak production of Brazilian quartz crystal was reached in 1943 when 2411 metric tons were exported. Minas Gerais, Goiaz, and Bahia are the principal producing states. Minor quantities are obtained from Espirito Santo and Northeastern Brazil.
Primary veins and pegmatites yield secondary deposits of eluvial, colluvial, and alluvial origin. The veins range in form from tabular or lenticular bodies, pipes, and pockets to composite lodes and bedded masses. The mineralogy is simple; accessory minerals are few and rare. A small proportion of clear crystals, occurring in vein masses of milky quartz, furnishes the commercial product. Filling, rather than replacement, is believed to be the dominant emplacement process. Pegmatites yield a little commercial quartz. Both residual (eluvial) and water-laid (alluvial) quartz deposits are economically important.
Crystals range up to 40 metric tons in weight; those of 1 to 5 tons occur in many deposits. Quartz from every locality studied is twinned on both the Brazil and Dauphiné laws. Phantoms are abundant.
Field studies reveal little difference between the final quartz from some pegmatites and that from veins. It is inferred that the veins may grade into pegmatites at depth and that both are products of the same mineralogenic epoch. Present evidence does not justify a closer dating for the formation of the veins and pegmatites than the early Paleozoic.
There are few large quartz mines in Brazil. The impressive quartz production during the war years came from many small, scattered workings. Mining methods are primitive, and mechanization was feasible in relatively few areas. The ratio of mine-clean crystal to the total quantity of excavated material varies between 1:1000 and 1:100,000, with an over-all average for the best mines of the order of 1:10,000. Cost of mining ranges from $2 to $10 a kilogram. The average export value during 1944 was $12.50 per kilogram.
The potential reserves of quartz crystal in Brazil are large, but actual or visual reserves in known districts are small. Future production capacity will be determined by economic factors.