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Ferric iron (Fe 3+) gives a pale yellow color in plagioclase feldspar from Lake County, Oregon. [18] The specific gravity increases smoothly with calcium content, from 2.62 for pure albite to 2.76 for pure anorthite, and this can provide a useful estimate of composition if measured accurately. [8]
Buddingtonite is an ammonium feldspar with the chemical formula: NH 4 AlSi 3 O 8. [25] ... The specific gravity in the plagioclase series increases from albite ...
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]
The formula may be written as Na 0.7-0.5 Ca 0.3-0.5 Al 1.3-1.5 Si 2.7-2.5 O 8. [2] The plagioclase feldspars are a continuous solid solution series and as such the accurate identification of individual members requires detailed optical study, chemical analysis or density measurements. Refractive indices and specific gravity increase directly ...
Labradorite ((Ca, Na)(Al, Si) 4 O 8) is a calcium-enriched feldspar mineral first identified in Labrador, Canada, which can display an iridescent effect . Labradorite is an intermediate to calcic member of the plagioclase series. It has an anorthite percentage (%An) of between 50 and 70. The specific gravity ranges from 2.68
Bytownite is a calcium rich member of the plagioclase solid solution series of feldspar minerals with composition between anorthite and labradorite.It is usually defined as having between 70 and 90%An (formula: (Ca 0.7−0.9 Na 0.3−0.1)[Al(Al,Si)Si 2 O 8]).
The composition of plagioclases is often expressed as a molar percentage of An%, or (for a specific quantity) An n, where n = Ca/(Ca + Na) × 100. [8] This equation predominantly works in a terrestrial context; exotic locales and in particular Lunar rocks may need to account for other cations, such as Fe 2+ , to explain differences between ...
Formula (repeating unit) ... Specific gravity: 2.5–2.6 ... Gridiron twinning distinguishes microcline from other feldspars. Distinguishable from plagioclase because ...