Search results
Results From The WOW.Com Content Network
Plagioclase displaying cleavage. (unknown scale) In volcanic rocks, fine-grained plagioclase can display a "microlitic" texture of many small crystals. Plagioclase (/ ˈ p l æ dʒ (i) ə ˌ k l eɪ s, ˈ p l eɪ dʒ-,-ˌ k l eɪ z / PLAJ-(ee)-ə-klayss, PLAYJ-, -klayz) [4] is a series of tectosilicate (framework silicate) minerals within the feldspar group.
Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. It represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula Na Al Si 3 O 8. It is a tectosilicate. Its color is usually pure white, hence its name from Latin, albus. [5]
A QAPF diagram is a doubled-triangle plot diagram used to classify intrusive igneous rocks based on their mineralogy. The acronym QAPF stands for "Quartz, Alkali feldspar, Plagioclase, Feldspathoid (Foid)", which are the four mineral groups used for classification in a QAPF diagram. The percentages (ratios) of the Q, A, P and F groups are ...
Solid solutions between albite and anorthite are called plagioclase, [14] or, more properly, plagioclase feldspar. Only limited solid solution occurs between K-feldspar and anorthite, and in the two other solid solutions, immiscibility occurs at temperatures common in the crust of the Earth. Albite is considered both a plagioclase and alkali ...
Plagioclase phenocrysts (white) and hornblende phenocryst (dark; intergrown with plagioclase) are set in a fine matrix of plagioclase laths that show flow structure. Rocks can be classified according to the nature, size and abundance of phenocrysts, and the presence or absence of phenocrysts is often noted when a rock name is determined.
Dacite consists mostly of plagioclase feldspar and quartz with biotite, hornblende, and pyroxene (augite or enstatite). The quartz appears as rounded, corroded phenocrysts, or as an element of the ground-mass. [3] The plagioclase in dacite ranges from oligoclase to andesine and labradorite.
Most anorthosite plutons are very coarse grained; that is, the individual plagioclase crystals and the accompanying mafic mineral are more than a few centimetres long. Less commonly, plagioclase crystals are megacrystic, or larger than one metre long.
Quartz (SiO 2) is present as more than 20% of the total quartz-alkali feldspar-plagioclase-feldspathoid content of the rock. [1] [2] Amphiboles and biotite are common in lesser quantities, while accessory minerals include apatite, magnetite and zircon. [3] [4] In older references tonalite is sometimes used as a synonym for quartz diorite.