Crystals have a nearly rectangular or square cross-section with slightly slanted dome and pinacoid terminations. Twinning is almost universal in all plagioclases. Crystals can be twinned according to the Albite, Carlsbad, Manebach and Baveno laws . Oligoclase can be found as a major rock forming component in granites and syenites. Cleavage is perfect in one and good in another direction forming nearly right angled prisms.
Fracture is conchoidal.
Hardness is 6 - 6.5. Streak is white. Associated Minerals are quartz , muscovite and K-feldspars . Lamellar twinning may cause a grooved effect on cystal and cleavage surfaces that appear as striations. Best Field Indicators are occurence, twinning striations, shimmer, density and index of refraction.