plagioclase

[ pley-jee-uh-kleys ]

noun

1. any of the feldspar minerals varying in composition from acidic albite, NaAlSi 3 O 8 , to basic anorthite, CaAl 2 Si 2 O 8 , found in most igneous rocks: shows twinning striations on good cleavage surfaces.

plagioclase

/ ˈpleɪdʒɪəʊˌkleɪz; ˌpleɪdʒɪəʊˈklæstɪk /

noun

1. a series of feldspar minerals consisting of a mixture of sodium and calcium aluminium silicates in triclinic crystalline form: includes albite, oligoclase, and labradorite

plagioclase

/ plā′jē-ə-klās′ /

1. Any of a series of common feldspar minerals, consisting of differing mixtures of sodium and calcium aluminum silicates. Plagioclase is typically white, yellow, or reddish-gray, but it can also be blue to black. It occurs in igneous rocks. The minerals albite, oligoclase, andesine, labradorite, bytownite, and anorthite are all plagioclases. Chemical formula: (Na,Ca)Al(Si,Al)Si 2 O 8 .

Derived Forms

• plagioclastic, adjective

Other Words From

• pla·gi·o·clas·tic [pley-jee-, uh, -, klas, -tik], adjective

Word History and Origins

Origin of plagioclase¹

First recorded in 1865–70; plagio- + -clase

Example Sentences

Maaz, which is on top and thus probably younger, has a composition similar to most basaltic lava flows — full of minerals known as pyroxene and plagioclase but with little or no olivine.

From Seattle Times

Séítah rocks contained evenly distributed crystals of the mineral olivine, which coalesce as magma slowly cools, whereas Máaz rocks had small grains of pyroxene and plagioclase, interlocked in a way that indicated igneous formation.

From Science Magazine

The texture of the rocks containing this mineral suggested that it formed from a large body of molten rock that cooled, and the light plagioclase crystals floated to the top.

From Scientific American

The researchers looked at samples of plagioclase and clinopyroxene from eastern Quebec, Canada and found that they contain magnetic needles approximately 50 to 100 nanometers in size, surprising the researchers.

From Fox News

Backlit under a microscope, minerals in the slices—including plagioclase, olivine, and pyroxene—burst into focus: polygonal islands swimming in a dark sea of rock.

From Science Magazine