It
is found in crystals, such as cubes, but mostly massive, botryoidal,
stalactiform, globular, or reniform, &c. The fracture is even,
sometimes running into concboidal or splintry; it is semi-transparent
or translucent, of little lustre, or dull; of white, gray, blue,
yellow, brown or greeu colors, which are all of a light shade, and
variously figured, striped, spotted, &c.
It scratches white glass, and has a specific gravity of 2.58 to 2.60. It is distinguished into the following varieties, viz.:
1. Chalcedony proper, or chalcedonyx, wherein white and gray stripes alternate with each other.
2. Mocha, or tree stones, are such chalcedonies as display black, brown, or red dendritical figures.
3.
Rainbow, or agate chalcedony, is chalcedony of thin and
concentric structure, which, cut across and kept towards the light,
displays an iridescence.
4. Cloudy chalcedony, has a light gray and transparent base, with dark and cloudy spots.
5. Plasma, dark grass-green. This mineral was very often employed by the ancients for cutting.
6. Semi-carnelian, or ceregat, is generally called the yellow chalcedony.
7. Sappharine, is the sky or sapphire blue chalcedony.
8. St. Stephen's stones, is the white chalcedony, with blood-red spots.
There
are many more varieties, and in my own collection I have polished
chalcedonies, among which, perhaps, as many again may be enumerated.
Chalcedony was originally procured from Chalcedon, in Asia Minor, whence its name.
Chalcedony
is found in gangues, and in the cavities of many rocks ; also in
boulders and pebbles. Localities exist in Saxony, Hungary, Faroe
Islands, Ceylon', on the shores
