[Chemical composition] The compositional change is large in the F:OH ratio, and the ratio varies depending on the conditions (production temperature) of the topaz varies from 3:1 to 1:1. From pegmatite → Yunyingyan → hydrothermal, the F:OH of topaz is from large to small. [Crystal structure] orthorhombic system; [Form] Columnar crystal form, common single shape is oblique square {110}, {120}, {021}; oblique double cone {111}, {221}, parallel double-sided {001}, {010}. The cylinder often has vertical stripes (Figure G-13). It is also often in the form of irregular granules and massive aggregates. Figure G-13 Topaz crystal [Physical properties] colorless or microstrip blue-green, yellow, milky white, tan or red-yellow; transparent; glass gloss cleavage parallel {001} complete. Hardness 8. The relative density is 3.52 to 3.57. [Cause and occurrence] Topaz is a typical gas-forming hydrothermal mineral under the condition of high temperature and volatile components. It is mainly produced in granitic pegmatite, Yunyingyan and high temperature gas-forming hydrothermal veins. [Identification features] columnar crystal form, the cross section is rhombus, the column has vertical lines, the cleavage {001} is complete, high hardness, which can be distinguished from similar quartz . [Main use] Transparent color beauty can be used as a gem material. Other bearings that can be used as abrasive materials and fine instruments. Die Casting Mold Base,Aluminium Die Casting,Die Casting Products,Cast Iron Molds Kun Shan Qi Dian Precision Mold Co., LTD , https://www.qidian-mold.com
a 0 = 0.465 nm, b 0 = 0.880 nm, c 0 = 0.840 nm; Z = 4. The structure of the crystal is composed of O 2- , F - , and OH - together as the four closest packing of ABCB (also called "double hexagonal" packing), and the stacked layer is parallel to (010). Al 3+ occupies an octahedral void to form an [AlO 4 (F, OH) 2 ] octahedron; Si 4+ occupies a tetrahedral void, and the composition [SiO 4 ] tetrahedron is isolated, with the aid of [AlO 4 (F, OH) 2 ] Octahedrons are linked.
Topaz (also known as Huang Jing)
Al 2 [SiO 4 ](F,OH) 2