According to the official records, there were registered in September 1906, 23,191 mining properties, of which very nearly five-sixths were described as producing s:'ver, either by itself or in combination with other metals: The properties were classed as 1572 gold, 5461 silver, 970 copper, 383 iron, 151 mercury, 94 lead, 86 sulphur, 52 antimony, 49 zinc, 40 tin, 21 opals, 9 manganese, 6 " sal gema," 5 tourmalines, i bismuth and i turquoise - the remainder being various combinations of these minerals.
Of growing importance are the gems found in California: a few diamonds in Butte county; rock crystal in Calaveras county; and tourmalines, kunzite, the rare pink beryl and bright blue topazes in San Diego county.
It possesses unlimited supplies, as yet not greatly exploited, of fine building stones, some oil and asphalt, and related bituminous products, a few precious and semi-precious stones (especially tourmalines, beryls and aquamarines found near Canyon near the Royal Gorge of the Arkansas river), rare opalized and jasperized wood (in the eastern part of the El Paso county), considerable wealth of lead and copper, enormous fields of bituminous coal, and enormous wealth of the precious metals.
The colors of aquamarine, peridot, citrine, amethyst, colored sapphires, tourmalines, iolites, and creamy freshwater pearls create an interplay with gold and diamonds that offers a refreshing and feminine appeal.
Some tourmalines change color slightly depending upon whether they are in natural or artificial light.