from The American Heritage® Dictionary of the English Language, 4th Edition
- n. A translucent to transparent milky or grayish quartz with distinctive microscopic crystals arranged in slender fibers in parallel bands.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. A form of fine-grained quartz that is nearly transparent or has a milky translucence; it fractures conchoidally.
from the GNU version of the Collaborative International Dictionary of English
- n. A cryptocrystalline, translucent variety of quartz, having usually a whitish color, and a luster nearly like wax.
from The Century Dictionary and Cyclopedia
- n. A cryptocrystalline variety of quartz, resembling in color milk diluted with water, and more or less clouded or opaque with veins, circles, or spots.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. a milky or greyish translucent to transparent quartz
There is a kind of onyx called a chalcedony, which hath the same qualities,  avails much against fantastic illusions which proceed from melancholy, preserves the vigour and good estate of the whole body.
As to the second, of which the name does not occur in treatises on gems, it may be identified with chalcedony, which is described as a sort of agate of an opaque quality, dimmed with clouds and flashing fires in the shadows.
Of the seven necklaces pictured here, all purchased recently, three are varieties of chalcedony, which is itself a type of microcrystalline quartz.
They were often made of semiprecious stones such as chalcedony, rock crystal, and lapis lazuli.
The many semi-precious stones which have a quartz basis (such as the varieties of waxy or cryptocrystalline chalcedony which is largely quartz in a very minutely crystalline condition) are often even tougher than the clear crystallized quartz.
The smooth edge of the circular disc is then charged with diamond dust and oil, the diamond dust being bedded into the edge of the metal disc by the pressure of some hard, fine-grained material, such as chalcedony, or rolled into the metal by the use of a rotating roller.
It was one of the stones on the breastplate of the high priest (Ex. 28: 20; R.V. marg., "chalcedony;" 39: 13).
"Or, again, if we borrow from Pope Innocent III. his ideas as to the mystical meanings of gems, we find that chalcedony, which is pale in the light and sparkles in the dark, is synonymous with humility; the topaz with chastity and the merit of good works, while the chrysoprase, the queen of minerals, implies wisdom and watchfulness.
Top lot will be the cover of a chalcedony cup dating from the 16th century, featuring Venus and Cupid cradled together within a scallop shell and framed by a silver gilt mount in the form of Jupiter as a swan.
From top: Siegelson antique archaeological revival gold and chalcedony brooch by Castellani, ca. 1880, price upon request, Siegelson, 212-832-2666; Bottega Veneta Milk silver bracelet $790 left and Magma silver bracelet $1,290 Bottegaveneta.com ; Stephen Russell Victorian 18k yellow gold agate pearl ruby and hard stone brooch, ca.