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Feldspar (/ ˈ f ɛ l (d) ˌ s p ɑːr / FEL(D)-spar; sometimes spelled felspar) is a group of rock-forming aluminium tectosilicate minerals, also containing other cations such as sodium, calcium, potassium, or barium. [3] The most common members of the feldspar group are the plagioclase (sodium-calcium) feldspars and the alkali (potassium ...
The middle part of this crystal sparkles, and usually the color is darkest in the middle and becomes lighter toward the outer edges. The feldspar which usually displays the aventurine appearance is oligoclase , though the effect is sometimes seen in orthoclase : hence two kinds of sunstone are distinguished as "oligoclase sunstone" and ...
Orthoclase, or orthoclase feldspar (endmember formula K Al Si 3 O 8), 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.
Alkali feldspar granite, some varieties of which are called 'red granite', [1] is a felsic igneous rock and a type of granite rich in the mineral potassium feldspar (K-spar). It is a dense rock with a phaneritic texture. The abundance of K-spar gives the rock a predominant pink to reddish hue; peppered with minor amounts of black minerals. [2] [3]
Its base colors include blue-gray, tan, and pink. Fine hematite inclusions are apparently responsible for the pink color. Very few of these potassium feldspar crystals are suitable as a gemstone because they are typically quite brittle and tend to break along cleavage during cutting. The source rock of this material is a biotite gneiss. [5]
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 to 2.72.
Sanidine is the high temperature form of potassium feldspar with a general formula K(AlSi 3 O 8). [2] Sanidine is found most typically in felsic volcanic rocks such as obsidian, rhyolite and trachyte. Sanidine crystallizes in the monoclinic crystal system. Orthoclase is a monoclinic polymorph stable at lower temperatures.
Appearance. move to sidebar hide. Help. This is a category for feldspar minerals, feldspar production, uses of feldspar, etc. Subcategories. This category has the ...