Chalcedony is a micro-crystalline variety of quartz occurring in several different forms, including onyx, agate, and jasper. It's chemical composition is silicon dioxide. Micro-crystalline are crystals that cannot be seen with the unaided eye. Micro crystalline minerals may appear massive or amorphous (no definite or clear shape or form) since no apparent crystal shape can be seen. It is in nodular forms, as smooth rounded pebbles, as banded masses, as amygdules, and as the linings of geodes.
In the gem and mineral trade, the name Chalcedony usually describes only white or blue Chalcedony, to distinguish it from the multicolored banded variety Agate and other unique varieties of this mineral. However, agates and jaspers are a variety of chalcedony.
Tree moss agate is a form of chalcedony. These form when impurities are present in the chalcedony. They may form a moss like growth in the mineral, forming what is known as Moss Agate. Most moss agate inclusions are comprised of iron or manganese oxide. These inclusions inhibit chalcedony banding that is characteristics in most agates.
Chalcedony can be found in many colors, white, blue, red, green, yellow, orange, brown, pink, purple, gray, black, colorless, and multicolored.
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