Chalcedony is a semi precious stone belonging to the cryptocrystalline variety of quartz in various shades of white, gray, yellow, brown, green and blue. Although it is usually transparent or translucent, some of the milk-white varieties are opaque. The color variations occur as a result of the presence of such impurities as iron, aluminum, and nickel. 

Chalcedony occurs as a lining or filling of cavities in rocks. The principal varieties are agate, which is banded and striped, having alternating layers of chalcedony and opal; jasper or other forms of quartz, carnelian which is clean and of various shades of red; chrysoprase, an apple green variety, in which the color is due to nickel oxide; heliotrope or bloodstone, of a dark green color with small spots of jasper; onyx, consisting of bands of opal and chalcedony of different colors, usually black and white; plasma, of a deep green color; and sardonyx, a red and white banded variety of chalcedony. The many colors and the high luster that chalcedony takes by polishing render it valuable for brooches, necklaces, and other ornaments, and some varieties are cut as seal stones. 

Chalcedony is found in many parts of the world. Superior varieties prized for gems are mined in Uruguay and in the Lake Superior area of the United States and Canada.

Magic & Myth

Varieties of chalcedony are believed to have the power to stabilize auras and balance polar energies. It is also said to  stimulate analytical capacities and awaken latent talents. It is believed to promotes marital fidelity and helps stress. It is also said to strengthen sight, heal mental illness, and help paralysis.