oligoclase
/ˈɒlɪɡə(ʊ)kleɪz
/noun [mass noun]
A feldspar mineral common in siliceous igneous rocks, consisting of a sodium-rich plagioclase (with more calcium than albite).It is composed of quartz, oligoclase, and microcline, with minor garnet, biotite, muscovite and iron-oxides....
- Here it was found sparsely as rounded grains associated with pargasite, diopside, oligoclase and lazurite.
- They range from bytownite - labradorite in basalts and gabbros, andesine - oligoclase in diorites and andesites to albite in granites and rhyolites.
Origin
Mid 19th century: from oligo- 'relatively little' + Greek klasis 'breaking' (because thought to have a less perfect cleavage than albite).