What is the difference between plagioclase and feldspar?
Plagioclase has a color range from white to dark gray, and it’s typically translucent. Alkali feldspar (also called potassium feldspar or K-feldspar) has a color range from white to brick-red, and it’s typically opaque. Many rocks have both feldspars, like granite.
What is the most effective way to differentiate between potassium feldspar and plagioclase feldspar?
What is the most effective way to differentiate potassium feldspar from plagioclase feldspar? Some cleavage planes of plagioclase feldspars have striations, whereas no potassium feldspars have striations.
Is orthoclase same as K-feldspar?
Orthoclase, or orthoclase feldspar (endmember formula KAlSi3O8), is an important tectosilicate mineral which forms igneous rock. The name is from the Ancient Greek for “straight fracture,” because its two cleavage planes are at right angles to each other. It is a type of potassium feldspar, also known as K-feldspar.
Why is K-feldspar pink?
K–feldspar albite intergrowths known as pertite and albite intergrowths K–feldspar as antipertite. The hardness is from 6 to 6.5 and the relative density of 2.55–2.63. The color is usually white, and sometimes changes from pale pink to reddish due to admixtures of iron (especially microcline).
How can you identify K-feldspar in a thin section?
In general, keys to identifying K-feldspar are its (lack of) color, its low birefringence, and its twinning. In thin section, microcline, orthoclase and sanidine are distinguished by their twinning, optical sign, and 2Vo.
What is the difference between plagioclase and orthoclase?
The key difference between orthoclase and plagioclase is that orthoclase appears in green-yellow colour, whereas plagioclase appears in white colour. Orthoclase and plagioclase are important minerals. Both these forms are members of the feldspar group.
Does granite contain K-feldspar?
All granites contain quartz and K-feldspar. If the K-feldspar is white, the granites are light gray; if the feldspar is pink or red, the granite is pink or red.
What Colour is plagioclase feldspar?
Color. Usually white, plagioclase feldspars can also be grey or brown. Labradorite is commonly dark blue or black and shows iridescent blue-red colors. Peristerite (see above) may show iridescence in pink or blue.
How do you identify K-feldspar?
Is plagioclase feldspar in granite?
The principal constituent of granite is feldspar. Both plagioclase feldspar and alkali feldspar are usually abundant in it, and their relative abundance has provided the basis for granite classifications.
Where is K-feldspar found?
K-feldspar is widespread and common in a wide variety of igneous and metamorphic rocks and in some sedimentary rocks.
Does granite contain K feldspar?
What mineral is K-feldspar?
Potassium feldspar refers to a number of minerals in the feldspar group, and containing potassium: Orthoclase (endmember formula KAlSi3O8), an important tectosilicate mineral that forms igneous rock. Microcline, chemically the same as orthoclase, but with a different crystalline structure.
What are facts about feldspar?
Grey feldspar is a striking blend of grey and tan shades with black inclusions
What is the chemical formula for plagioclase?
When a particular Plagioclase Feldspar cannot be identified, it is simply called “Plagioclase” or “Plagioclase Feldspar”. The percentages of sodium and calcium for each member listed above are an approximate value; the actual percentage can vary as much as 20 percent. Chemical Formula. (Na,Ca)Al1-2Si3-2O8.
What are the special properties of feldspar?
▣ Plagioclase Feldspar. These minerals have a triclinic structure. ▶ Anorthite – It is mostly found in igneous rocks,and used in making ceramics and cement.
What is the formula for feldspar?
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