Though all types contain eight oxygen atoms in their structure, calcium containing varieties of this mineral, which has labradorite and microcline varieties, have two atoms of both silicon and aluminum and (*) K-varieties only possess a single silicon atom.
One member of this mineral class exhibits an optical phenomenon also known as the Schiller effect, in which light refracts within layered ingrowths formed during the mineral's cooling process. After twinning, another mineral in this class exhibits a distinct grating structure when viewed under a polarizing microscope. Though all types contain eight oxygen atoms in their structure, calcium containing varieties of this mineral, which has labradorite and microcline varieties, have two atoms of both silicon and aluminum and (*) K-varieties only possess a single silicon atom. The striated varieties of this mineral are the major component of the rocks of the lunar highlands, form the continuous branch of Bowen's Reaction Series, and are known as plagioclase. The most abundant type of mineral on Earth, for 10 points, identify this class of silicate minerals whose orthoclase variety acts as the exemplar for a Mohs hardness of six.
One member of this mineral class exhibits an optical phenomenon also known as the Schiller effect, in which light refracts within layered ingrowths formed during the mineral's cooling process.
{feldspars}