The particular feldspar that furnishes most of the moonstone is orthoclase, a silicate of potassium and aluminum.
In syenite and greenstone it occurs more commonly than orthoclase.
orthoclase and microcline feldspar are used in the manufacture of porcelain and chinaware.
This curve would represent the conditions under which orthoclase is in equilibrium with the molten magma.
The felspar ranges from bytownite to oligoclase, being usually a variety of labradorite; orthoclase is scarce.
The turbidity of orthoclase is usually due to partial kaolinization.
If the initial composition of the magma is represented by a point between the two eutectic points, orthoclase will separate first.
The china-clay rocks of Cornwall and Devon are granites in which the orthoclase has become kaolinized.
There is also some variation in the amount of quartz present, and in the relative importance of the orthoclase and plagioclase.
Examples of substances exhibiting these three kinds of dispersion are borax, orthoclase and gypsum respectively.