[Chemical composition] In addition to Mg, Fe is completely homogeneous, and there are secondary isomorphisms such as Fe3+, Mn, Ca, Al, Ti, Ni, etc., Figure G-2. Figure G-2 Composition of the olivine minerals (According to Cornelius S et al., 1977; cited in Pan Zhaoyu, 1993) [Crystal structure] orthorhombic system; Figure G-3 shows the crystal structure of olivine in the form of a coordination polyhedron (quoted from Pan Zhaoyu et al., 1993) The M position in the olivine structure can also be divided into two categories, one at the M1 position, at the center of symmetry, and the other half at the M2 position, on the symmetry plane, for the olivine Mg 2 [SiO4]-Fe 2 [SiO 4 ] series. , Mg, Fe into the order of M1, M2 - disorder can be used as a characterization feature. Olivine and spinel are all AB 2 X 4 type compounds in terms of composition. Both of the cations also occupy 1/8 of the tetrahedral voids and 1/2 of the octahedral voids in the structure, but the structure of the two is different. The most obvious difference is that the former O 2- is the most closely packed hexagonal, which is oblique. The crystal system; in the latter, O 2- is the most closely packed cubic, belonging to the equiaxed crystal system. Secondly, the connection between the tetrahedron and the octahedron in the two structures is also significantly different. The famous crystal chemist Bernal (1936) first proposed that under the pressure conditions of the mantle, the olivine structure can be transformed into a tighter spinel structure with a density 9% higher than that of olivine. the above. Experiments have also shown that as the pressure increases, the olivine structure can be transformed into a spinel-like structure, which in turn transforms into a spinel-type structure (the negative percentage in the formula represents the amount of volume reduction after structural transformation): 130×10 8 Pa145×10 8 Pa>600km deep α-Mg 2 [SiO 4 ]—-------------——————--——→β-Mg 2 [SiO 4 ]———→γ-Mg 2 [ SiO 4 ]———→2MgO+SiO 2 Peridot-8%±like spinel-29% spinel rhombohedite quartz [Form] The crystal is columnar or thick plate (see Figure G-4). However, it is rare to have a good crystal form, and it is generally irregularly shaped like a grain-like aggregate (Fig. G-5). Figure G-4 Crystals of olivine (cited from Pan Zhaoyu et al., 1993) Parallel double-sided : a{100}, b{010}, c{001}; slanted square: m{110}, l{120}, d{101}, n{011}, g{021}; Oblique double cone: o{111} Figure G-5 granular olivine crystals [Physical properties] Forsterite is white, light yellow or light green, with the increase of Fe 2+ content in the composition, the color deepens to dark yellow to dark green or black, the general olivine is olive green; glass luster; transparent to translucent. Cleavage {010} medium; common shell-like fracture. Hardness 6.5 to 7. The relative honeyness increased with the increase of Fe 2+ content (3.27~4.37). [genesis and occurrence] Olivine is mainly produced in the ultra-basic, basic magmatic rocks and skarn and metamorphic rocks rich in Mg. It is the main component of mantle rock and the main component of meteorite. Among them, forsterite is an important mineral of magnesium skarn. It is generally considered that olivine is a kind of SiO 2 unsaturated mineral, so it is produced under the condition of Mg-rich Si and does not co-exist with quartz, namely: Mg 2 [SiO 4 ]+SiO 2 →Mg 2 [Si 2 O 6 ] However, in the skarn, the olivine Fe 2 [SiO 4 ] can be symbiotic with quartz. Olivine is easily altered by hydrothermal action and weathering, and the common product is serpentine. The olivine in the wild has been serpentine and has become a residual crystal or an illusion. [identification characteristics] characterized by its characteristic olive green, granular, poor cleavage, shell-like fracture, can also be identified according to the occurrence. [Main use] Magnesium-rich olivine can be used as magnesia refractory; transparent, coarse grain (8mm or more) can be used as gem material, such as the deep source inclusion of Zhangjiakou alkaline basalt in China, there is a gem material grade. Olivine output. Mini-Prism Striped Acrylic Sheet Jiangmen Kunxin new Material Technology Co.,Ltd , https://www.jmkunxinplastics.com
Wherein forsterite Mg 2 [SiO 4]: a 0 = 0.475nm, b 0 = 1.020nm, c 0 = 0.598nm; fayalite Fe 2 [SiO 4]: a 0 = 0.482nm, b 0 = 1.048nm , c 0 =0.609 nm. Z=4. Olivine is a single island silicate, so O 2- can achieve the closest closest packing. From the point of view of stacking, the structure can be regarded as O 2 - parallel to (100) as the approximate hexagonal closest packing, and Si 4 + fills 1/8 of the tetrahedral void to form [SiO 4 ] tetrahedron, outside the backbone The cation M fills 1/2 of the octahedral voids to form a [MO 6 ] octahedron. From the coordination polyhedral coupling method, in each of the parallel (100) coordination octahedrons, half is a solid octahedron (filled by M), and the other half is a hollow octahedron (not filled with M). Both are jagged chains with a difference of b/2 in position; solid octahedrons between layers are opposite to hollow octahedrons, adjacent layers are connected by shared octahedral apex, and alternating layers are shared [SiO 4] tetrahedra vertices and edges (each of [SiO 4] tetrahedra in the three edges and 6 shared octahedral) associated (FIG. G-3).
(Mg,Fe) 2 [SiO 4 ]