Bantase istitaniaAnother kind of isomorphic mineral.Chemical composition: TiOtwo, containing 59.95% titanium.Orthorhombic system.It is trihedral with rutile and anatase.The crystals are plate and leaf shaped.Light yellow, brown to black, streaked light yellow, light gray to brown, transparent or translucent,Adamantine lusterOr semi metallic luster.
Bantase mainly occurs in the Alpine vein in metamorphic rocks, but also in hydrothermal alteration, contact metamorphism and placer ores.
Chinese name
Brookite
Foreign name
Brookite
Profile
The crystals are plate shaped, light yellow, brown to black
BantaseOrthorhombic systemIn the crystal structure of brookite, O forms distorted four layers most closelyStacking, layer parallel to (100) crystal plane, Ti inoctahedral void , each [TiOsix]The octahedron has three edges and angles with the surrounding three [TiOsix]Octahedron share, these shared edges and corners are shorter than other edges and corners, Ti slightly deviates from the center of the octahedron, forming a distorted octahedron.[TiOsix]The octahedron is parallel to the c-axis to form a zigzag chain, and the chain and the chain are connected in parallel (100) to form a layer.
chemical property
The molecular formula of brookite is also the same as that of rutile, and the chemical formula is TiOtwo，Ti 59.95%，O 40.05%。The composition contains a small amount of Fe3+, sometimes FetwoOthreeUp to 4.5%;Containing a small amount of NbtwoOfiveAnd TatwoOfive。Only plate crystals are distinguished from rutile and anatase.In the composition, Ti can be3+、Nb5+、Ta5+Replace.Those rich in Fe are called iron plate titanium ore, and those rich in Nb are called niobium plate titanium ore.
physical property
The brookite crystal is in the shape of plate and blade.The color is light yellow, brown to black.Stripes are light yellow, light gray to brown.Transparent or translucent.Diamond luster or semi metallic luster.Mohs hardness is 5.6~6.Density 3.9~4.1g/cmthree。
optical properties
It is yellowish brown, golden brown or reddish brown in the thin section, withAbnormal interference color, very high protuberance.Biaxial crystal (positive gloss), parallel extinction.High refractive index: np=2.583，nm=2.584～2.586，ng=2.700～2.741，ng- np=0.117~0.156, weak polychromaticity, ng: bright yellow, light greenish brown, nm: bright yellow, orange brown, np: colorless, olive, yellow brown.Under the reflected light, the slate in the light sheet is gray, and the unique growth cone can be distinguished according to the darker color.
Optical characteristics
Yellowish brown, reddish brown or brownish black;Yellow brown or golden brown in thin slices.Polychromatic weak np- orange, light yellowish brown, nm- orange purple brown, ngA lemon yellow, purple brown.Absorption: ng> nm>npOr nm>ng>np。Positive pole high protrusion.The roughness is very significant.The interference color is high white, and sometimes abnormal interference color can be seen, so that no real extinction can be seen anywhere.Bicrystal along (120) plane.indicatrix dispersion Extremely strong, cross axial dispersion.For red light and yellow light, the optical axis plane is parallel to (001), and the role dispersion of the optical axis is r<v;For blue light and green light, the optical axis plane is parallel to (010), and the role dispersion of the optical axis is r>v;For yellow green light, the optical axis angle is 0 °.
Optical orientation and 2V vary with temperature.When the optical axis plane is parallel to (001) under the illumination of a fixed wavelength light source, the temperature decreases and 2V decreases;When the optical axis plane is parallel to (010), the temperature decreases and 2V increases.[2]
Genetic occurrence
Bantase is a hydrothermal mineral, coexisting with quartz, albite, sphene, rutile, anatase, etc., which forms later than rutile and earlier than anatase.Bantase is stable under natural conditions and is common in ores.[3]
Source of atlas: Materials Research and Testing Center of Wuhan University of Technology
Transformation of brookite
Announce
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Change: When the temperature is about 700 ℃, the content of Bantasite can be changed torutile。
Identification characteristics: special optical property, extremely high refractive index and birefringence, and extremely strong dispersion are excellent identification characteristics of brookite.Rutile has goodcleavage And prismatic shape;The refractive index of ferrotitanium (Pseudoarkansasite) is low, the optical axis angle is large, and there is no significant dispersion;Goethite is reddish brown and has negative light property, which is different from that of brookite and can be distinguished.[2]
