How do you identify orthoclase in the thin section?

How do you identify orthoclase in the thin section?

Orthoclase is frequently known as potassium feldspar or K-spar, and is easily distinguished from the plagioclase feldspars in hand sample by its lack of striations. In thin section, alkali feldspar grains often look like they’re sprinkled with dirt (PPL) or tiny confetti (XPL).

What is orthoclase used for?

Orthoclase is used in the manufacture of glass and ceramics; occasionally, transparent crystals are cut as gems. Orthoclase is primarily important as a rock-forming mineral, however, and is abundant in alkali and acidic igneous rocks, in pegmatites, and in gneisses.

How can plagioclase be detected in the thin section?

Hardness (6-6.5) and cleavage are good indicators of a plagioclase as opposed to other similar silicates. In thin section or grain mount, the general lack of pleochroism and the twinning are good indicators. The presense of parallel striae on cleavage surfaces distinguishes plagioclase from K-feldspar.

Where is orthoclase found?

granite
Orthoclase, also known as alkali feldspar or K-feldspar, is one end-member of a solid solution between orthoclase and albite. Orthoclase is found in silica-rich igneous rocks such as granite, and in high grade metamorphic rocks.

How is orthoclase made?

Most orthoclase forms during the crystallization of a magma into intrusive igneous rocks such as granite, granodiorite, diorite, and syenite. Significant amounts of orthoclase are also found in extrusive igneous rocks such as rhyolite, dacite, and andesite.

What minerals is orthoclase made of?

It is a type of potassium feldspar, also known as K-feldspar. The gem known as moonstone (see below) is largely composed of orthoclase….

How can you tell 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.

What is the product of orthoclase?

Together with the other potassium feldspars, orthoclase is a common raw material for the manufacture of some glasses and some ceramics such as porcelain, and as a constituent of scouring powder. Some intergrowths of orthoclase and albite have an attractive pale luster and are called moonstone when used in jewellery.

What is the luster of orthoclase?

VitreousOrthoclase / Luster

What is orthoclase?

Orthoclase is one of the ten defining minerals of the Mohs scale of mineral hardness, on which it is listed as having a hardness of 6. NASA ‘s Curiosity Rover discovery of high levels of orthoclase in Martian sandstones suggested that some Martian rocks may have experienced complex geological processing, such as repeated melting.

Why is cleavage difficult to see in thin section of orthoclase?

It can be difficult to see cleavage in thin section due to orthoclase’s low relief. Distinguishable from microcline by a lack in gridiron twinning. Distinguishable from sanidine by a larger 2V x. Orthoclase, or orthoclase feldspar ( endmember formula K Al Si 3 O 8 ), is an important tectosilicate mineral which forms igneous rock.

How big is a ton of orthoclase?

It measured ~10×10×0.4 m and weighed ~100 tons. Together with the other potassium feldspars, orthoclase is a common raw material for the manufacture of some glasses and some ceramics such as porcelain, and as a constituent of scouring powder.

How is orthoclase different from microcline and sanidine?

Distinguishable from microcline by a lack in gridiron twinning. Distinguishable from sanidine by a larger 2V x. Orthoclase, or orthoclase feldspar ( endmember formula K Al Si 3 O 8 ), is an important tectosilicate mineral which forms igneous rock.