[Rose quartz] gets its pale-red color from the presence of a small amount of titanium. It is widely distributed, but is more abundant in the Black Hills of South Dakota.
Aventurine is quartz which has inclosed tiny scales of mica or hematite giving it a spangled appearance.
[Prase] is a green quartz, the color being due to the inclusion of fibrous crystals of green actinolite.
Cat’s Eye is a quartz which has inclosed silky fibers of asbestos. When this is cut parallel to the fibers, the effect is opalescent. The colors are greenish, yellowish-gray, and brown. This form, however, is not to be confused with the true or Oriental Cat’s Eye, which is chrysoberyl and has the hardness of 8.
[Chalcedony]
SiO₂
Non-crystalline, occurring in botryoidal, stalactitic or concretionary masses; hardness, 7; specific gravity, 2.65; color white when pure; luster waxy; translucent to transparent on thin edges.
In addition to the crystalline form, silica is freely deposited in an amorphous or cryptocrystalline form which has the same properties as quartz, except the crystal faces. This is called chalcedony, and it occurs in seams, cavities and free surfaces. When the surface of a chalcedony deposit is free it has a waxy luster. It is generally very brittle and breaks in a peculiar splintery manner. Like quartz it also has a great many varieties, according to the impurities present. Its wide distribution, hardness, and the manner in which it can be chipped have made this a most important stone in the history of the development of civilization. The early men first broke it into rough tools, such as knives, axes, spear points, etc., and used these as cutting tools, of one sort or another, because they held their edge better than most stones. We apply, to the people who used only these chipped stones as tools, the term “Men of the Old Stone Age,” or the period is termed the Palæolithic Age. Later men learned how to grind the edge to a smoother outline, and this much shorter period is termed the Neolithic Age. The use of flints for the first tools is world-wide, and the American Indian when discovered was still using chalcedony in its rough-hewn state.
“There the ancient Arrow-maker
Made his arrow heads of sandstone,
Arrow heads of chalcedony,