Onyx
Onyx
List of municipalities in Valladolid
<catset>Category="Gemstones"</catset><catset>Category="Quartz varieties"</catset><dl> <dt><dd><i>This article is about the mineral. See <a href="Onyx (disambiguation)">Onyx (disambiguation)</a> for other meanings</i> </dl> [image] <b>Onyx</b> is a banded variety of <a href="Chalcedony">Chalcedony</a>, a cryptocrystalline form of <a href="Quartz">Quartz</a>. The colours of its bands are white and black. It is usually cut as a <a href="Cabochon">Cabochon</a>, or into beads, and is also used for <a href="Intaglio">intaglios</a> and <a href="Cameo">cameos</a>. Some onyx is natural but much is produced by the staining of <a href="Agate">Agate</a>.<p><table border=1><tr><td> <caption>Technical details</caption> </td></tr><tr><td>Chemical composition and name</td><td>SiO<SUB>2</SUB> - <a href="Silicon dioxide">Silicon dioxide</a></td></tr><tr><td>Hardness (<a href="Mohs scale of mineral hardness">Mohs scale</a>)</td><td>7</td></tr><tr><td><a href="Relative density">Specific gravity</a></td><td>2.65 - 2.66</td></tr><tr><td><a href="Refractive index">Refractive index</a> (R.I.)</td><td>1.543 - 1.552 to 1.545 - 1.554</td></tr><tr><td><a href="Birefringence">Birefringence</a></td><td>0.009</td></tr><tr><td>Optic sign</td><td>Positive</td></tr><tr><td>Optical character</td><td>Uniaxial</td></tr></table><p><h2 style="margin: 0; padding-top: 0.5em; padding-bottom: 0.17em; border-bottom: 1px solid #aaaaaa; font-size: 150%;">See also</h2><ul><li><a href="List of minerals">List of minerals</a> </ul>