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<p>have both lower densities and indices of refraction than quartz. The transformation from ?-quartz to <a href="page.php?w=beta-quartz">beta-quartz</a> takes place abruptly at 573&nbsp;°C. Since the transformation is accompanied by a significant change in volume, it can easily induce fracturing of ceramics or rocks passing through this temperature limit. The high-pressure minerals, <a href="page.php?w=seifertite">seifertite</a>, <a href="page.php?w=stishovite">stishovite</a>, and <a href="page.php?w=coesite">coesite</a>, though, have higher densities</p><p>
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