A chalcedony that occurs in bands of different colors and is used as a gemstone, especially in cameos and intaglios.(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "onyx" in a sentence
"The high altar, composed of Mexican marble and onyx, is one of the finest ever constructed."
"The onyx was the color of her long, shiny black hair; the rubies were the color of her lips."
"It is found notably in the volcanic district of Mono County, and elsewhere, sometimes in the form of Mexican onyx, which is only a translucent variety of the same marble."