Anatase; octahedritetitania（TiOtwo）One of the three minerals in the mineral.It occurs in veins in igneous rocks and metamorphic rocks, and also in placer deposits. It is hard, shiny square crystal system with different colors.Many anatase is formed by the weathering of sphene, and it can be altered into rutile itself;TiOtwoThe isomorphic substitution includes Fe, Sn, Nb, Ta, etc.In addition, it is also found thatrare earth elementAnd U, Th. The crystal forms are generally cone, plate and column.
It is produced inigneous rockandMetamorphic rockInternalLodeMedium, usually also appears inplacerIn the bed, it is hard and shinyTetragonal systemCrystal, with different colors.The famous vein deposits occur in many areas of the Alps.Many anatase minerals are composed ofSpheneIt is formed by weathering and can be altered intorutile；RutileHomomorphic illusion(i.e., metasomatic products with the same shape) are common in clastic deposits in Brazil and Mount Wula.IsomorphismSubstitutions include Fe, Sn, Nb, Ta, etc.In addition, it is also found thatrare earth elementAnd U, Th.[1]
Crystal formIt is generally in the shape of cone, plate and column.
Anatase TiO2
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Crystal chemical properties
Anatase, rutile and brookite areHomomorphic multiimage, i.e. composition andrutile、BrookiteSame, but different crystal structure.Anatase belongs to tetragonal crystal system, and its crystal structure is similar to the frame shape. O ions are the most closely packed cubic, and Ti atoms are located inoctahedral void 。[TiOsix]Octahedrons are connected with each other by sharing two pairs of opposite edges, [TiOsix]The octahedron surrounds each fourth spiral axis to form a spiral chain parallel to the c-axis.Ti coordination number is 6 and O coordination number is 3.The Ti-O atom spacing is 0.1937nm and 0.1964nm, and the O-O atom spacing is 0.2802nm and 0.3040nm.
chemical property
Anatase has the same chemical composition as rutile, and its chemical formula is TiOtwo, isomorphism replaces Fe, Sn, Nb, Ta, etc.In addition, it is also found that the anatase contains Y group based rare earth elements, U and Th.[3]
physical property
The crystal forms are generally cone, plate and column.The color is brown, yellow, light green blue, light purple, gray black, and occasionally nearly colorless.Stripes are colorless to light yellow.Adamantine luster。Complete cleavage.Mohs hardness is 5.5-6.5.Density 3.82~3.976g/cmthree。
optical properties
Differentcolour, mainly brown, yellow, light green blue, light purple, gray black, occasionally nearly colorless.Uniaxial crystal (negative phototropism), sometimes biaxial crystal with small optical axis angle.Refractive indexVery high with obvious changes, such as yellow crystal, refractive index: nzero=2.501；Grey crystal, nzero=2.556, weak polychrome, dark crystal with strong polychrome, strong wine yellow crystal, no: dark wine yellow, ne: Light red light brown.Under reflected light, anatase in the light sheet is gray, with obvious internal reflection, gray band blue, no double reflection and reflection polychromism, and reflectance ratiosphaleriteSlightly higher.
Genetic occurrence
Anatase is relatively unstable, and changes intorutileThe formation conditions are similar to rutile.It occurs in veins of igneous rocks and metamorphic rocks, and also in placer deposits. It is hard, shiny, and has different colors.Anatase also occurs in metamorphic hydrothermal sedimentary rocks. The titanium deposit in Yangtizi Moshishan, Zhenglan Banner, Inner Mongolia is a new type found in China in recent yearsTitanium depositYangtizishan ore belt is a hydrothermal reworked titanium rich deposit, and Moshishan ore belt is a sedimentary metamorphic titanium rich deposit.The main features of these two ore beltsUseful mineralIt is anatase, rutile and ilmenite.Many anatase is formed by the weathering of sphene, and it can be altered into rutile itself.The rutile formed by replacement of anatase has the illusion of anatase, which is very common in clastic deposits in Brazil and Mount Wula.In cassiterite sulfide ores, anatase is commonly associated with cassiterite.[3]
Optical characteristics
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Brown, yellow and black, and a few are blue and green gray;The thin village is colorless, or light yellow, light brown, or distributed unevenly or in a ring band.With weak polychromaticity: noOne yellow, blue and green;neA brown, dark blue, sky blue.The dark variety may be more polychromatic.Absorption usually no<ne, sometimes no>ne。The positive pole has high protrusion and obvious roughness.The refractive index changes obviously.Such as yellow anatase crystal no=2.501，ne=2.431；Grey product no=2.556。The interference color is very high, reaching Grade IV or above, parallel extinction or symmetric extinction.Double crystal edge (112), rare.Negative ductility.The dark variety may be a biaxial crystal with a small optical axis angle.[4]
Transformation and identification of anatase
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Change: Anatase is TiOtwoA low temperature homomorphic polymorphous variant.It can be transformed from other titanium minerals, and rutile can be transformed at 800-900 ℃.
Identification characteristics: sharp biconical shape, high positive protrusion, and axial negative product are its identification characteristics.The differences between rutile and brookite are: (1) rutile is in the form of uniaxial orthomorphic, columnar and acicular crystals;(2) Bantase is axial orthomorphic, and the crystal is in parallel (001) plate and column shape.[4]
