Andalusite
Andalusite
Cocteau Twins
<catset>Category="Silicate minerals"</catset>[image] <b>Andalusite</b> is an <a href="Aluminium">Aluminium</a> <a href="Silicate minerals">nesosilicate</a> <a href="Mineral">Mineral</a> with the chemical formula Al<sub>2</sub>SiO<sub>5</sub>.<p>The variety <a href="Chiastolite">Chiastolite</a> commonly contains dark inclusions of carbon or clay which form an <i>X</i> or a cross in section.<h2 style="margin: 0; padding-top: 0.5em; padding-bottom: 0.17em; border-bottom: 1px solid #aaaaaa; font-size: 150%;">Occurrence</h2>Andalusite is a common regional <a href="Metamorphism">metamorphic</a> mineral which forms under high pressure and/or temperature. The minerals <a href="Kyanite">Kyanite</a> and <a href="Sillimanite">Sillimanite</a> are <a href="Polymorph">polymorphs</a> of andalusite, each occurring under different temperature-pressure regimes and are therefore rarely found together in the same rock. Because of this the three minerals are a useful tool to help identify the pressure-temperature paths of the host rock in which they are found.<p>It was first reported from <a href="Andalusia">Andalucia</a>, <a href="Spain">Spain</a>. in 1789.<h2 style="margin: 0; padding-top: 0.5em; padding-bottom: 0.17em; border-bottom: 1px solid #aaaaaa; font-size: 150%;">Details</h2><table><tr><td bgcolor=ffc0c0><a href="Crystal structure">Crystallographic system</a></td><td><a href="Orthorhombic">Orthorhombic</a></td></tr><tr><td bgcolor=ffc0c0>Colours</td><td>Brown, green, pink, violet and red varieties</td></tr><tr><td bgcolor=ffc0c0>Lustre</td><td></td></tr><tr><td bgcolor=ffc0c0><a href="Mohs scale of mineral hardness">Hardness</a></td><Td>7.5</td></tr><tr><td bgcolor=ffc0c0><a href="Relative density">Specific gravity</a> </td><td>3.13 - 3.17</td></tr><tr><td bgcolor=ffc0c0><a href="Refractive index">Refractive index</a> </td><td>1.641-1.648</td></tr><tr><td bgcolor=ffc0c0><a href="Cleavage (crystal)">cleavage</a></td><td>3</td></tr><tr><td bgcolor=ffc0c0><a href="Crystal twinning">Twinning</a></td><td>Lamellar</td></tr><tr><td bgcolor=ffc0c0><a href="Pleochroism">Pleochroism</a></td><td>Clear to patchy pink </td></tr></table><p><h2 style="margin: 0; padding-top: 0.5em; padding-bottom: 0.17em; border-bottom: 1px solid #aaaaaa; font-size: 150%;">Related minerals</h2><ol> <li><a href="Kyanite">Kyanite</a> <li><a href="Sillimanite">Sillimanite</a> <li><a href="Chiastolite">Chiastolite</a> </ol><h2 style="margin: 0; padding-top: 0.5em; padding-bottom: 0.17em; border-bottom: 1px solid #aaaaaa; font-size: 150%;">References</h2><ul> <li><font color=#700070> Mineral galleries</font> <li><font color=#700070> Webmineral</font> <li><font color=#700070> Mindat w/ locations</font> </ul>