A shock-induced polymorph of anatase and rutile from the Chesapeake Bay impact structure, Virginia, U.S.A.

Jackson, J. C.; Horton, J. Wright; Chou, I-Ming; Belkin, Harvey E.

doi:10.2138/am.2006.2061

Cited by 35 publications

(21 citation statements)

References 22 publications

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“…However, our experiments show that even at pressures of 10-23 GPa and temperatures of 1 500-1 800 ℃, SiO 2 solubility in rutile is still quite limited, with a maximum of 5.3 wt.% at 2 000 ℃ and 23 GPa, much lower than the high Si-rutile reported by Yang et al (2003). In nature, rutiles formed at ultrahigh pressures in metamorphic belts (Hwang et al, 2000) and shocked craters (Jackson et al, 2006;Goresy et al, 2001a, b) have structures similar to α-PbO 2 and ZrO 2 phases. They are all believed to form at high pressures but low temperatures (T<1 000 ℃ ).…”

Section: Discussionmentioning

confidence: 50%

SiO2 solubility in rutile at high temperature and high pressure

et al. 2009

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Silicon-bearing rutile has been found in chromitite from the Luobusa (罗布莎) ophiolite, Tibet. However, the extent of SiO 2 solubility in rutile and the nature of its origin are still unclear. At high pressure, SiO 2 takes a rutile structure with Si in 6-fold coordination. Thus, high pressures may enhance its solubility in rutile because of possible isovalent exchange in the octahedral site. In this study, we report new experimental results on SiO 2 solubility in rutile up to 23 GPa and 2 000 ℃. Starting materials were mixtures of powdered pure rutile and pure quartz, with compositions of (Ti 0.5 Si 0.5 )O 2 , (Ti 0.93 Si 0.07 )O 2 , and (Ti 0.75 Si 0.25 )O 2 . The mixtures were loaded into either platinum capsules (for a 10/5 assembly) or rhenium capsules (for an 8/3 assembly). The experiments were carried out using multi-anvil high-pressure apparatus with a rhenium resistance heater. Sample temperatures were measured with a W5%Re-W26%Re thermocouple and were controlled within ±1 ℃ of the set temperature. TiO 2 -rich and SiO 2 -rich phases were produced in all the quenched samples. Microprobe analyses of the phases show that the solubility of SiO 2 in rutile increases with increasing pressure, from 1.5 wt.% SiO 2 at 10 GPa to 3.8 wt.% SiO 2 at 23 GPa at a temperature of 1 800 ℃. The solubility also increases with increasing temperature from 0.5 wt.% SiO 2 at 1 500 ℃ to 4.5 wt.% SiO 2 at 2 000 ℃ at a pressure of 18 GPa. On the other hand, the solubility of TiO 2 in coesite or stishovite is very limited, with an average of 0.6 wt.% TiO 2 over the experimental P-T ranges. Temperature has a much larger effect on the solubility of SiO 2 in rutile than pressure. At high pressure, the melting point of SiO 2 is definitely higher than that of TiO 2 and the eutectic point moves towards SiO 2 in the TiO 2 -SiO 2 system. Lower oxygen fugacity decreases the solubility of SiO 2 in rutile, whereas water has little effect on the solubility. Our experimental data are extremely useful for determining the depth of origin of the SiO 2 -bearing rutile found in nature.

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Section: Discussionmentioning

confidence: 50%

SiO2 solubility in rutile at high temperature and high pressure

et al. 2009

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“…We can assume that in our TiO 2 :Er material, erbium induces a slight structural deformation which gives origin to new Raman bands in a similar way as in Refs. [21] and [23].…”

Section: Resultsmentioning

confidence: 99%

Red shifts of the Eg(1) Raman mode of nanocrystalline TiO2:Er monoliths grown by sol–gel process

et al. 2015

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“…The formation of natural TiO 2 -II could be related to highpressure endogenic geological processes or bolide impact events. Occurrence of natural TiO 2 -II had been previously reported in ultrahigh-pressure metamorphic rocks [11,12], mantle-derived rocks [13], terrestrial impact structures [14][15][16], and tektite [17]. However, the mineralogical features and the formation conditions of natural TiO 2 -II still needs to be further investigated because of the very limited material that had been found.…”

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High-pressure polymorph of TiO2-II from the Xiuyan crater of China

Chen

Xie

et al. 2013

Chin. Sci. Bull.

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Abundant TiO 2 -II, a high-pressure polymorph of titanium dioxide, was found in the gneiss fragments of impact-produced breccias from the Xiuyan crater. Rutile in the gneiss was severely fragmented and fine-grained clasts less than 2 m in size had been transformed to TiO 2 -II. Irregular thin layered TiO 2 -II is also observed in coarse-grained rutile fragments, where the TiO 2 -II layers distributes along fractures and cracks in rutile. About 30 percent of rutile in the gneiss had been transformed to TiO 2 -II. Fine grains of TiO 2 -II display light bluish grey to light yellow brown in plane-polarized reflected light. Crystallographic investigation shows that TiO 2 -II has an orthorhombic structure with space group Pbcn. The cell parameters are a=4.543(1) Å, b=5.491(9) Å and c=4.895(2) Å. Its empirical formula calculated on the basis of two oxygen atoms can be written as (Ti 0.985 Fe 0.008 Nb 0.006 -Si 0.003 Zr 0.001 ) 1.003 O 2 , or simply formula TiO 2 . According to the shock effects of quartz and feldspars, the peak shock pressure and post-shock temperature in the TiO 2 -II-bearing gneiss are estimated to be between 35 and 43 GPa and 300-900°C, respectively. The finding of TiO 2 -II in the shock-metamorphosed gneiss provides another mineral physics evidence for shock origin of the Xiuyan crater. Rutile, a titanium dioxide, is a common accessory mineral in various types of rocks. At high pressure, rutile can be transformed into high-pressure polymorphs of TiO 2 -II (-PbO 2 ), baddeleyite, orthorhombic I and cotunnite phases with increasing pressure [1]. High-pressure polymorphs of baddeleyite, orthorhombic-I and cotunnite-type TiO 2 reverse to TiO 2 -II on decompression. TiO 2 -II is the only highpressure polymorph that can be recovered experimentally at ambient conditions [2]. i  - had been firstly synthesized by static compression experiment [3]. A number of static compression experiments succeed in the transition of rutile to TiO 2 -II at pressure range between 4 and 12 GPa and temperature between 400 and 1500°C [3][4][5][6][7]. Shock-loading experiments revealed that rutile transforms to i  - at peak shock pressure from 20 to 100 GPa [8][9][10]. The formation of natural TiO 2 -II could be related to highpressure endogenic geological processes or bolide impact events. Occurrence of natural TiO 2 -II had been previously reported in ultrahigh-pressure metamorphic rocks [11,12], mantle-derived rocks [13], terrestrial impact structures [14][15][16], and tektite [17]. However, the mineralogical features and the formation conditions of natural TiO 2 -II still needs to be further investigated because of the very limited material that had been found.The Xiuyan crater is a recently confirmed impact structure in China. The target rocks of the crater were shock-metamorphosed, from which impact-produced breccia, coesite, planar deformation features in quartz have been identified [18][19][20]. In this paper, we report the occurrence and mineralogical features of TiO 2 -IIin the impact-produced breccias

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A shock-induced polymorph of anatase and rutile from the Chesapeake Bay impact structure, Virginia, U.S.A.

Cited by 35 publications

References 22 publications

SiO2 solubility in rutile at high temperature and high pressure

SiO2 solubility in rutile at high temperature and high pressure

Red shifts of the Eg(1) Raman mode of nanocrystalline TiO2:Er monoliths grown by sol–gel process

High-pressure polymorph of TiO2-II from the Xiuyan crater of China

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