A cubic polymorph of this mineral, cristobalite, forms metastable spheres that, when hydrated, form opal.
A cubic polymorph of this mineral, cristobalite, forms metastable spheres that, when hydrated, form opal. One stone made of this mineral and moganite is monoclinic and has a characteristic waxy luster and is called chalcedony. Another form of this mineral, citrine, is generated upon heating a stone with iron and aluminum impurities that give it a purple color, amethyst. FTP, identify this mineral commonly found along with gold, a silicon dioxide crystal defining Mohs hardness seven and known for its rose and milky varieties.
A cubic polymorph of this mineral, cristobalite, forms metastable spheres that, when hydrated, form opal.
{quartz}