Anorthite
Anorthite
Augment (linguistics)
<catset>Category="Silicate minerals"</catset><b>Anorthite</b> is one of the <a href="Feldspar">plagioclase</a> feldspars, an important group of <a href="Mineral">minerals</a> abundant in the Earth's crust. Anorthite's chemical formula is CaAl<sub>2</sub>Si<sub>2</sub>O<sub>8</sub>.<h2 style="margin: 0; padding-top: 0.5em; padding-bottom: 0.17em; border-bottom: 1px solid #aaaaaa; font-size: 150%;">Mineralogy</h2>Anorthite is the <a href="Calcium">Calcium</a>-rich endmember of the plagioclase system, the other endmember being <a href="Plagioclase">albite</a> (<a href="Sodium">Sodium</a>-rich). The range of intermediate compositions have varying ratios of calcium and sodium <a href="Ion">ions</a>.<h2 style="margin: 0; padding-top: 0.5em; padding-bottom: 0.17em; border-bottom: 1px solid #aaaaaa; font-size: 150%;">Occurrence</h2>Anorthite occurs in <a href="Igneous rock">igneous</a> and <a href="Metamorphism">metamorphic</a> rocks. Its <a href="Biological type">type localities</a> are Monte Somma and Valle di Fassa, <a href="Italy">Italy</a>,<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>Triclinic</td></tr><tr><td bgcolor=ffc0c0>Colours</td><td>Normally colourless or white, colourless in thin section.</td></tr><tr><td bgcolor=ffc0c0>Lustre</td><td>Vitreous</td></tr><tr><td bgcolor=ffc0c0><a href="Mohs scale of mineral hardness">Hardness</a></td><Td>6-6.5</td></tr><tr><td bgcolor=ffc0c0><a href="Refractive index">Refractive index</a> </td><td>1.51</td></tr><tr><td bgcolor=ffc0c0>Cleavage</td><td>3: 1 perfect, 1 good, 1 poor</td></tr><tr><td bgcolor=ffc0c0>Twinning</td><td>Multiple lamellar and Carlsbad twins</td></tr><tr><td bgcolor=ffc0c0><a href="Pleochroism">Pleochroism</a></td><td>Yellow to dark green to transparent to opaque</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="Feldspar">Feldspars</a> <li><a href="List of minerals">List of minerals</a> </ul><h2 style="margin: 0; padding-top: 0.5em; padding-bottom: 0.17em; border-bottom: 1px solid #aaaaaa; font-size: 150%;">External link</h2><ul> <li><font color=#700070> WebMineral entry</font> </ul>