Idine石石(Sanidine)

Orthoclase

Microcline

K[AlSi ₃ O ₈ ](Or)

[Chemical Composition] The composition of the three K-feldspars contains a certain amount of Ab molecules and less than 5% to 10% of An molecules, and occasionally may contain a very small amount of Cn molecules. A small amount of Fe ³⁺ may be substituted for Al in the feldspar and the micro-plagioclase. Further, trace amounts of Mg, Fe ²⁺ , Sr, Pb, and Mn ^{2+ may} be present to replace Ca or Ba in the An or Cn molecule.

[Crystal structure] Their space group and unit cell parameters are shown in Table 21-8, and their crystal structures are the same (see the feldspar family overview). The only difference is the order degree and the three slopes, that is, the feldspar is high temperature. In disordered state, the order degree is close to zero, the three-slope is zero; the feldspar is partially ordered, the order degree is greater than zero, and the three-slope is zero. However, some people think that feldspar has ultra-microscopic The continuous structure is composed of a super-microscopic twin or unit cell domain with three-slope symmetry, and a monoclinic crystal in the optical rotation. In this sense, its three-slope It should be greater than zero; micro-plagioclase is a low-temperature ordered state, and the degree of order and three slopes are greater than zero.

Figure G-48 lattice sodium double crystal combined with sodium albite

(quoted from Pan Zhaoyu et al., 1993)

(a) in the micro-plagioclase; (b) in the feldspar

Figure G-49 feldspar crystal

[Form] Potassium feldspar with the crystallization temperature from high to low, the feldspar → feldspar → micro plagioclase series, the shape also correspondingly from the parallel {010} plate → parallel c axis column → parallel The evolution of the columnar axis of the a-axis. In addition, the feldspar and feldspar common Casbah double crystal, the micro plagioclase double crystal is more complicated, in addition to the common Kasbah, also can be seen Manny Baba, Bavinor, and, slightly oblique Feldspar usually has lattice twin crystals composed of sodium feldspar law and Xiao Na feldspar law. In the micro plagioclase lattice twin crystal, the Sodium feldspar law bimorph junction is parallel to the b-axis and is almost vertical (001 ), while the sodium feldspar law double crystal junction is (010), and thus is also nearly perpendicular to (001), so it can be seen at (001) that the two sets of polycrystalline twins intersect in a lattice shape with a close angle At 90°. Similar lattice twins are also found in 歪 feldspar (see below), but the Sodium feldspar stellite joint is parallel to the b-axis and nearly vertical (100), so it can only be seen on the (100) plane. Polycrystalline twin-crystal lattice (Figure G-48). The different twin crystal types of feldspar, feldspar and micro-plagioclase are also related to their degree of ordering. As mentioned in the overview of the Changshi family, the ordering changes the crystal structure from monoclinic to monoclinic. During the three-slanting process, the spheroidal law is formed by the different orientation deformation of the unit cell, and the shale-feldspar feldspar law is the twin crystal. Therefore, the micro-plagioclase with the highest degree of ordering is most likely to appear in the above two twin crystals. The coexisting lattice twins, while the least ordered perlite is not easy to appear, and the ultramicroscopic twins in feldspar are likely to be less ordered (Fig. G-49).

[Physical properties] feldspar colorless and transparent, feldspar, micro plagioclase is often meat red, light yellow or grayish white; glass luster, sometimes plexisphere on the cleavage surface; The stone is yellow; the transparency is high, similar to glass. {001} and {010} are completely cleaved. Hardness 6 to 6.5. The relative density is 2.55 to 2.63. According to the difference in morphology and physical properties, there are several variations:

Advertia: See the overview of the feldspar.

Amazonite: Green, about the color of the Tianhe stone, some people think it is caused by Rb, some people are attributed to Fe, others are considered to contain Pb, and some people explain the coloration of lattice defects. According to research by the former Soviet scholar Ostranov (МНОстроумов, 1982), the cause of green is caused by Pb and Fe.

Perthite: The K-feldspar and the albite slab formed by the dissolution of the solid solution due to the temperature drop, forming a "striped feldspar". These strips are visible on the (010) section, they are distributed in the direction of [106] and are at an angle equal to 73° to the (001) plane.

Moonstone:

If the potassium and albite phases in the striped feldspar form a microscopic layered structure, a beautiful "floating" effect, called moonstone, is produced.

In addition, a characteristic structure can be seen in pegmatite, called "graphical structure", which is a regular continuum composed of quartz and micro-plagioclase (or feldspar). Figure G-50(a)). It can be seen from the section that it is like an ancient hieroglyph, so it is called "text structure" (Fig. G-50(b)). It is formed by simultaneous crystallization of feldspar and quartz in the residual melt. The "text structure" is actually an interplay phenomenon in which feldspar and quartz form a similar surface network.

(a) (b)

Figure G-50 Image Structure Formation Mechanism

(quoted from Pan Zhaoyu et al., 1993)

(a) Orientation rule of feldspar and quartz (the [001] crystal rib of feldspar and the crystal plane between the α-quartz rhombohedron and the cylinder [11 3] crystal lattice uniform); (b) text structure feldspar crystal face: C (001), B (010), M (110); quartz crystal face: m (10) 0), r (10 1), r' (01 1)

[genesis and occurrence] Translucent feldspar is one of the main rock-forming minerals of medium-acid volcanic rocks , especially in coarse shale . The feldspar and micro-plagioclase are the main light-colored rock-forming minerals in the medium-acid and alkaline igneous rocks. Corresponding volcanic rocks contain more feldspars, while pegmatites and Changying rocks are dominated by micro-plagioclase. In the metamorphic rocks, the deep metamorphic rocks are dominated by orthorhombic rocks; in the shallow metamorphic belts, most of them are micro-inclined feldspars. In the contact metamorphic zone, potassium feldspar, which was originally formed at a lower temperature, may sometimes be converted into a feldspar. The feldspar debris contained in the sedimentary rocks depends on the feldspar species of the original rock. Micro-plagioclase and feldspar can be formed during the autogenous process. Potassium petrochemicals in the hydrothermal alteration process are common on both sides of high-temperature quartz veins, as seen in the quartz veins of many black tungsten deposits in the Nanling area of ​​China, mostly micro-plagioclase.

[Identification features] The hand specimens are usually identified as transparent, colorless or flesh-red, with two sets of orthogonal or nearly orthogonal cleavage. As for the identification of various species in K-feldspar, it can be distinguished by using twin crystals and occurrences, but the more reliable identification should use X-ray, spin-light data, and order degree.

[Main use] See the overview of the Changshi people.

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