The name usually given to alkali feldspars which have a chemical composition ranging from Or₄₀Ab₆₀ to Or₁₀Ab₉₀± up to approximately 20 mole % An (Or, Ab, An = KAlSi₃O₈, NaAlSi₃O₈, CaAl₂Si₂O₈) and which deviate in one way or another from monoclinic symmetry tending toward triclinic symmetry. When found in nature, they usually do not consist of a single phase but are composed of two or more kinds of K- and Na-rich domains mostly of submicroscopic size. In addition, they are frequently polysynthetically twinned after either or both of the albite and pericline laws. It appears that they originally grew as the monoclinic monalbite phase inverting and unmixing in the course of cooling during geological times. They are typically found in lavas or high-temperature rocks.