Autogenous mineral of silica

Opal: opal is made by separating SiO2 from an aqueous solution and dehydrating colloid, so it is amorphous and has high water content (up to 10%). In the thin section, opal is colorless and transparent, with increased negative projections. Due to the dispersion effect, the contact between opal and gum or quartz is yellow. No cleavage. Total extinction under the orthogonal mirror. Opal is easily mixed with volcanic glass debris, but the glass debris has a unique shape, and its refractive index is not less than 1.490. Opal is also easy to mix with analcime, but analcime has cleavage. The difference from fluorite is that fluorite has a crystalline form and separation. Opal is a quasi-stable mineral, easy to recrystallize and transform into chalcedony. Therefore, it only exists in young strata. Chalcedony: Chalcedony is a cryptocrystalline SiO2 mineral crystallized from opal, so it is a transitional type between opal and quartz. In thin slices, chalcedony is colorless and transparent, with opposing protrusions. Under an orthogonal microscope, fibrous crystals can be seen, forming petal or fan-shaped aggregates. When rotating the animal platform, the chalcedony fibers reach the extinction position in the sequence, and the extinction shadow moves in a wavy manner. This extinction characteristic is called fan-shaped extinction. Sometimes chalcedony is a spherical aggregate with cross-extinction. Grade I gray interference color, mainly parallel extinction. Fogg once proposed paying particular attention to a type of authigenic chalcedony in carbonate rocks, which can be used to determine sedimentary and diagenetic environments. Fogg divided this type of chalcedony into negative ductile chalcedony (negative chalcedony), positive ductile chalcedony (positive chalcedony), water chalcedony, and mottled chalcedony. The former is a product of freshwater environment sedimentation or metasomatism; generally, chalcedony belongs to this category. The latter three types of chalcedony may have been directly precipitated by SiO2 in an evaporative environment or formed by SiO2 metasomatized and evaporating minerals. If you are looking for high quality, high purity and cost-effective silicon dioxide, or if you require the latest price of silicon dioxide, please feel free to email contact mis-asia.