Beryl is, chemically, a silicate of aluminum and glucinum, Be₃Al₂(SiO₃)₆. It usually forms in hexagonal crystals. When there is also in the stone some oxide of chromium, it becomes a bright or a deep green: this is the emerald.
The word beryl covers a large number of hard and lustrous stones. At first it was applied to clear crystals; thus in the fifteenth century we find references to “water clear as beryl.” A pale bluish-green variety of beryl is the aquamarine. A yellow variety is the chrysoberyl (chrysos is the Greek word for gold).
Carnelian
The carnelian was originally the cornelian. Because of its flesh color, the name was changed under the influence of the Latin word for flesh, carnem. Carnelian is a red variety of chalcedony.
Cat’s-eye
There are two varieties of the cat’s-eye, equally effective against evil spirits. The stone may be either olive green, or reddish brown. The most attractive shades are bamboo and moss green. The distinguishing feature of the stone is that it seems to have a horizontal slit that sends back a white band of light, moving with the stone, and resembling the gleam in the baleful eye of a cat. Other appropriately sinister colorings are sometimes called tiger’s-eye and hawk’s-eye. The Oriental cat’s-eye is a mineral of the chrysoberyl group; the Occidental, somewhat less glinting, is a variety of quartz.
The cat’s-eye, of course, is in wide repute for the power it confers of seeing in the dark. Thus it is an excellent stone for hunters. But it proves similarly effective in mental darkness, providing the power for seeing through the schemes of connivers. Wearing a cat’s-eye may thus save one from becoming a cat’s-paw. I met a detective recently who was wearing a superb hawk’s-eye ring; he told me he had just received notice of his promotion, “with distinction,” to the rank of captain.
Chalcedony
Chalcedony is the name of a large group of stones, variously colored, consisting mainly of non-crystal quartz. It has the lustre of wax. Chalcedony has been known from early times and is mentioned in the Bible. Among the stones belonging to this group are agate, carnelian, chrysoprase, jasper, onyx, and sard.