Noun
Common or potash feldspar crystallizing in the monoclinic system and having two cleavages at right angles to each other. See Feldspar.
Source: Webster's dictionaryComposition of syenites The feldspar component of syenite is predominantly alkaline in character (usually orthoclase ). Source: Internet
Cleavage, parting, fracture, and tenacity main Perfect basal cleavage as seen in biotite (black), and good cleavage seen in the matrix (pink orthoclase ). Source: Internet
This then causes orthoclase and biotite, both K rich minerals into which Rb can substitute, to precipitate. Source: Internet
Feldspar (Amazonite) Perthite is either microcline or orthoclase with thin lamellae of exsolved albite. Source: Internet
In the acid rocks the common feldspars are orthoclase, perthite, microcline, and oligoclase—all having much silica and alkalis. Source: Internet
Leucite is very rare in plutonic masses; many minerals have special peculiarities in microscopic character according to whether they crystallized in depth or near the surface, e.g., hypersthene, orthoclase, quartz. Source: Internet