sardonyx, a variant of onyx in which the colored bands are sard, or red, rather than black

stone geological geology mineralogy mineral natural massive rough ore nugget black green red faceted aluminosilicate quartzous beautiful raw silicate nature jewel calcite yellow strip slice stripe chalcedony striped geodes streak streaky marble semiprecious stripy tabby surface pattern opal onyx gem sardonyx precious texture agate background variant colored bands sard black