- Feldspar Feld"spar`, Feldspath Feld"spath`, n. [G.
feldspath; feld field + spath spar.] (Min.)
A name given to a group of minerals, closely related in
crystalline form, and all silicates of alumina with either
potash, soda, lime, or, in one case, baryta. They occur in
crystals and crystalline masses, vitreous in luster, and
breaking rather easily in two directions at right angles to
each other, or nearly so. The colors are usually white or
nearly white, flesh-red, bluish, or greenish.
Note: The group includes the monoclinic (orthoclastic) species orthoclase or common potash feldspar, and the rare hyalophane or baryta feldspar; also the triclinic species (called in general plagioclase) microcline, like orthoclase a potash feldspar; anorthite or lime feldspar; albite or soda feldspar; also intermediate between the last two species, labradorite, andesine, oligoclase, containing both lime and soda in varying amounts. The feldspars are essential constituents of nearly all crystalline rocks, as granite, gneiss, mica, slate, most kinds of basalt and trachyte, etc. The decomposition of feldspar has yielded a large part of the clay of the soil, also the mineral kaolin, an essential material in the making of fine pottery. Common feldspar is itself largely used for the same purpose.
The Collaborative International Dictionary of English. 2000.