QUARTZ.
QUARTZ CRYSTALS.
This mineral comprises about one half the earth’s crust. Its symbol is SiO₂, being a compound of silicon and oxygen, in the proportions indicated. It is very hard, easily scratching glass, of which it forms an important constituent, is acted upon by only one acid—hydrofluoric; this attacks it eagerly, as may be shown by the following interesting experiment: Take a little lead saucer, or in the absence of this, spread lead foil carefully over the inside of an ordinary saucer, and in this place some powdered fluor spar. This mineral is quite abundant in nature, and is always to be obtained, in the form of a powder, from dealers in chemicals. Have a pane of glass covered by a thin film of wax. Now trace upon this surface with a sharp point, anything you may desire, verse or picture. Pour into the saucer containing the fluor spar, sufficient sulphuric acid to make a paste. Place over this the plate of glass, with the waxed side down, and let it remain for twenty-four hours. Remove the wax by heating, and on the glass you will find a perfect etching, the HF having removed the silica.
The same effect may be produced in a few moments by applying to the bottom of the saucer a moderate heat. Care should be taken not to inhale the fumes, as they are highly corrosive.
Quartz can be melted at a high temperature, and may be dissolved in certain hot solutions. It is still a question in dispute, whether the numerous quartz veins found in rocks were introduced there in melted form or in solution. Probably, sometimes in one state and sometimes in the other. Any visitor to a glass manufactory can see how easily glass in a melted state is manipulated; and travelers often bring from the geysers[1] fine specimens of silica called geyserite, derived from the material held in solution in the hot water, and deposited on the edge of the “basin.”
SIDE AND TOP VIEW OF THE REGENT OR PITT DIAMOND (REDUCED IN SIZE)—CUT IN THE FORM OF THE “BRILLIANT.”
Quartz may be classified under two varieties—the common and the rare. Sand, pebbles, many conglomerates, all sandstone rocks come under the former head. The old red sandstone described by Hugh Miller,[2] in which fossil fish are so abundant, and the new red sandstone of the Connecticut valley, famous for its bird or reptile tracks, brought to light through the labors of Dr. Hitchcock,[3] were formed of sand cemented together under pressure by the peroxide of iron. There are many beautiful varieties of the rarer forms of quartz. Not a few of these were known to the ancients, as may be seen by reading the twenty-first chapter of Revelations, where a number are mentioned in the description of the heavenly city. “The wall of it was of jasper, and the foundations of the wall of the city were garnished with all manner of precious stones. The first foundation was jasper; the second, sapphire; the third, a chalcedony; the fourth, an emerald; the fifth, a sardonyx; the sixth, sardius; the seventh, chrysolite; the eighth, beryl; the ninth, a topaz; the tenth, a chrysoprasus; the eleventh, a jacinth; the twelfth, an amethyst.”
All of these excepting the sapphire, which is crystallized alumina, are either pure or mixed varieties of quartz, colored with some metallic oxide. One of the most beautiful forms of these precious stones is the agate, especially that kind called the onyx, which consists of a succession of opaque and transparent layers. When carved into gems, this is called the cameo. A wonderful carved cameo was in the Tiffany exhibit at the Centennial Exposition, valued at four thousand dollars. The several layers were so cut as to represent a man looking through the bars of his prison.