These stones are much softer than original and the majority of carved calcite stone sold in the markets is currently referred to as onyx stone. Banded calcite stones found in countries such as India and Mexico are also referred to as onyx stones. However, artificial treatments are carried out on onyx stones in order to give the black coloration to black onyx and the red and yellow coloration in sardonyx. The most famous variety of it is black onyx, but, it is not commonly found in comparison to it with colored bands. Sardonyx is another type of it wherein, the band coloration is in shades of red as opposed to black which is more commonly found in it. Onyx stone is cryptocrystalline and consists of intergrowths of silica based minerals such as quartz and moganite.
It is formed with bands of chalcedony displaying alternating colors. This with controlled banding are referred to as Cave Onyx and Mexican Onyx. This is a general name given to other forms of banded stone such as alabaster, marble, obsidian, and opal.
Onyx stone normally contain either black or white colored bands. The colors possessed by these bands vary in each stone and can range from white to almost any other color. It is worthwhile noting that agate stone and is also banded forms with the only difference being that while agate possesses curved bands and it has parallel bands. An onyx stone is a parallel banded variety of silica mineral.
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