| Onyx is a semi-precious form of chalcedony which has alternating straight bands of color, most commonly brown, red, white, and black. Chalcedony is the group name for a large family of stones, all of which form from silicon dioxide, also known as quartz. In order to be classed as chalcedony, a stone must be milky, and translucent to transparent, often with layers or bands of color. The color of onyx, as with other forms of chalcedony, is created through impurities which seep into the rock as it forms. |
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