Feldspar

The English name oligoclase, also known as orbite, is one of the members of the plagioclase isomorphic series, consisting of 90% to 70% albite and 10% to 30% calcite molecules; in addition, a small amount of potassium feldspar can be found. Often white to gray, even flesh red, gray green. Two axis negative crystals, - 2V = 82o +. The refractive index ng = 1.541 ~ 1.552, NM = 1.536 ~ 1.548, NP = 1.532 ~ 1.545, fold ratio 0.007 - 0.010. The relative density is 2.62 to 2.67, and the hardness is 6 ~ 6.5. It is mainly found in the intermediate acidic igneous rocks, and is also the main constituent mineral of many metamorphic rocks. In the widely distributed feldspar, only a few of them have the effect of the sun stone effect or Moonstone effect, which can be used as gemstones. They are called "more feldspar" and "more feldspar Moonstone".
The basic structural unit of feldspar is tetrahedron. It consists of 4 oxygen atoms surrounded by a silicon atom or aluminum atom. Each tetrahedron shares an oxygen atom with another tetrahedron, forming a three-dimensional skeleton. The large radius of alkali or alkaline earth metal cations is located in the large gap within the skeleton, and the coordination number is 8 (in the monoclinic feldspar) or 9 (in the three diagonal feldspar). Most feldspar crystals are plate shaped or columnar along a crystalline axis. Twinning is very common. There are more than 20 kinds of twin crystals. Common are sodium long stone law, the law of man's law, Bawinno's law, and the double crystal of Xiao Na Chang Shi law. They are found in three oblique crystals or monoclinic and three oblique crystals respectively. Feldspar is usually milky white, but it is often dyed with yellow, brown, light red, dark grey and so on. Some can also have beautiful color change or faint color. There are two groups of cleavage, with an angle of 90 degrees (monoclinic) or near 90 degrees (87 degrees) (three diagonal system). The proportion between 2.56 and 2.76 increased with the increase of An content and decreased with the increase of Or. The moth hardness is 6 ~ 6.5. The feldspar rich in potassium or sodium is mainly used in the ceramic industry, the glass industry and the enamel industry. The feldspar containing rare elements such as rubidium and cesium can be used as a mineral material for the extraction of these elements, and the beautiful feldspar of color can be used as a decorative stone and a secondary gem.
The most common mineral in the earth's crust is feldspar, which is also found on the moon and meteorites. Within the depth of 15 km underground, feldspar accounts for 60% of the total crustal weight. Feldspar is the main constituent of igneous rock, and is also common in metamorphic rocks and sedimentary rocks. Feldspar is a kind of aluminosilicate mineral containing calcium, sodium and potassium. It has many kinds, such as albite, calcite, barium feldspar, barium feldspar, micro plagioclase, ortho feldspar, and feldspar. They all have glassy luster, various colors, colorless, white, yellow, pink, green, gray, black and so on. Some are transparent and some are translucent. Feldspar itself should be colorless and transparent. It is colored or not completely transparent because it contains other impurities. Some are lumpy, some are plate shaped, some are columnar or needle shaped. Usually in igneous rocks and metamorphic rocks, the feldspar is very small, only 0.1 to 10 millimeters, up to 5~10 centimeters in the porphyry, and some in the pegmatite of some tens of meters. Feldspar is a raw material for ceramics and glass industry. Some feldspars have beautiful colourful or faint colors, and can be used as gem materials.