1. Oligoclase is a high sodium feldspar crystallizing in the triclinic system.2. The distinctive texture of rapakivi granite is due to oligoclase rims on orthoclase phenocrysts. 3. The accessory minerals of these rocks are principally oligoclase , muscovite, apatite and zircon. 4. Oligoclase is also found in metamorphic rocks formed under transitional greenschist to amphibolite facies conditions.5. The feldspar is usually orthoclase, but can also be albite, oligoclase or microcline. 6. The main feldspar in mugearite is oligoclase . 7. Its reddish mass includes large crystals of potassium feldspar surrounded by green rings of oligoclase . 8. "' Oligoclase "'is a rock-forming mineral belonging to the plagioclase feldspars. 9. The feldspar ranges from bytownite to oligoclase , being usually a variety of labradorite; orthoclase is scarce. 10. The feldspar of the granulites is mostly orthoclase or cryptoperthite; microcline, oligoclase and albite are also common.
