Chalcedony

Chalcedony is a cryptocrstalline form of silica, composed of very fine intergrowths of the minerals quartz and moganit. These are both silica miners, but they differ in that quartz has a trigonal crystal structure, whilst moganite is monoclinic. It can assume a wide range of colours, but those most commonly seen are white to gray, grayish-blue or a shade of brown ranging from pale to nearly black.

Chalcedony and its named varieties are well represented in various birthstone charts and can be found for all the months except January, April, and November. It is also listed as a birthstone for all the Zodiac signs except Taurus, Cancer, Scorpio and Sagittarius.
The term chalcedony is derived from the name of the ancient Greek town Chalkedon in Asia Minor.

Chalcedony, which is found worldwide, is the name for a group of stones made of a microcrystalline or cryptocrystalline variety of quartz, which means the quartz crystals are too small to be seen without high magnification.

In jewelry usage, the name Chalcedony is usually applied only to the light blue translucent and waxy form. Other stones in this group are know as agate, Petrified dinosaur bone, bloodstone, petrified wood, woodfire agate, carnelian, sardonyx, tiger’s eye, chrysocolla, oxyx and chrysoprase.