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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]
Albite is considered both a plagioclase and alkali feldspar. The ratio of alkali feldspar to plagioclase feldspar, together with the proportion of quartz , is the basis for the QAPF classification of igneous rock.
The intergrowth forms by exsolution due to cooling of a grain of alkali feldspar with a composition intermediate between K-feldspar and albite. There is complete solid solution between albite and K-feldspar at temperatures near 700 °C and pressures like those within the crust of the Earth, but a miscibility gap is present at lower temperatures ...
Potassium feldspar does form a solid solution series with albite, due to the identical charges of sodium and potassium ions, which is known as the alkali feldspar series. Thus, almost all feldspar found on Earth is either plagioclase or alkali feldspar, with the two series overlapping for pure albite.
Feldspar (amazonite) Perthite is either microcline or orthoclase with thin lamellae of exsolved albite. Amazon stone, or amazonite, is a green variety of microcline. It is not found anywhere in the Amazon Basin, however. The Spanish explorers who named it apparently confused it with another green mineral from that region.
Oligoclase is a rock-forming mineral belonging to the plagioclase feldspars. In chemical composition and in its crystallographic and physical characters it is intermediate between albite (Na Al Si 3 O 8) and anorthite (CaAl 2 Si 2 O 8). [1] The albite:anorthite molar ratio of oligoclase ranges from 90:10 to 70:30.
Anorthite is the calcium-rich endmember of the plagioclase solid solution series, the other endmember being albite (NaAlSi 3 O 8). Anorthite also refers to plagioclase compositions with more than 90 molecular percent of the anorthite endmember.
The rock of Salem, Massachusetts, United States, is a mica-foyaite rich in albite and aegirine: it accompanies granite and essexite. Litchfieldite is another well-marked type of nepheline-syenite, in which albite is the dominant feldspar. It is named after Litchfield, Maine, United States, where it occurs in scattered blocks. Biotite ...