Onyx

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Onyx

Postby shottheradio » Jul 16, 2007 11:39 pm

What is true onyx? I'm not talking about Onyx marble/mexican onyx. True onyx, I always thought was black and white banded chalcedony? true or false?
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Re: Onyx

Postby Caverdale » Jul 17, 2007 12:26 am

shottheradio wrote:What is true onyx? I'm not talking about Onyx marble/mexican onyx. True onyx, I always thought was black and white banded chalcedony? true or false?


My understanding from college minerology classes was that onyx was banded chalcedony, but the bands can be of any colors. In fact, I think black and white only is unusual, but I'm often wrong.
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Re: Onyx

Postby Teresa » Jul 17, 2007 8:43 am

Caverdale wrote:
shottheradio wrote:What is true onyx? I'm not talking about Onyx marble/mexican onyx. True onyx, I always thought was black and white banded chalcedony? true or false?


My understanding from college minerology classes was that onyx was banded chalcedony, but the bands can be of any colors. In fact, I think black and white only is unusual, but I'm often wrong.


About the same here: I just looked in 3 rock books and 1 gem book: the definition seems to be any relatively straight, wide banded gem-quality chalcedony of alternating colors (as opposed to agate, which often has a circular aspect). Sardonyx always has alternating white and red (white chalcedony and sard, aka carnelian) bands. "Onyx" or "black onyx" usually is cut with the grain of the bands, with an intricate carving in the white part, and the white removed so that the black is the background. Used historically for men's signet rings. Sardonyx is used in the same way for women's cameo carvings.

Bottom line: it's all chalcedony quartz. The calcite onyx superficially looks like the other (banded flowstone) but is too soft and brittle to be used for jewelry.
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Postby shottheradio » Jul 17, 2007 6:22 pm

thanks for the replies. I did some research on it myself. I've also read that "true onyx" is going to be black and white. "onyx" is any banded chaledony and "sard onyx" is white and red. thats what I have basically broke it down to.
thanks again.
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