Chen Ming, Shu Jinfu, Mao Ho-kwang, Xie Xiande, Hemley Russell J
Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Wushan, Guangzhou 510640, China.
Proc Natl Acad Sci U S A. 2003 Dec 9;100(25):14651-4. doi: 10.1073/pnas.2136599100. Epub 2003 Nov 25.
A high-pressure polymorph of chromite, the first natural sample with the calcium ferrite structure, has been discovered in the shock veins of the Suizhou meteorite. Synchrotron x-ray diffraction analyses reveal an orthorhombic CaFe2O4-type (CF) structure. The unit-cell parameters are a = 8.954(7) A, b = 2.986(2) A, c = 9.891(7) A, V = 264.5(4) A3 (Z = 4) with space group Pnma. The new phase has a density of 5.62 g/cm3, which is 9.4% denser than chromite-spinel. We performed laser-heated diamond anvil cell experiments to establish that chromite-spinel transforms to CF at 12.5 GPa and then to the recently discovered CaTi2O4-type (CT) structure above 20 GPa. With the ubiquitous presence of chromite, the CF and CT phases may be among the important index minerals for natural transition sequence and pressure and temperature conditions in mantle rocks, shock-metamorphosed terrestrial rocks, and meteorites.
在随州陨石的冲击脉中发现了铬铁矿的一种高压多晶型物,这是首个具有钙铁石结构的天然样本。同步辐射X射线衍射分析揭示了一种正交晶系的CaFe₂O₄型(CF)结构。晶胞参数为a = 8.954(7) Å,b = 2.986(2) Å,c = 9.891(7) Å,V = 264.5(4) ų(Z = 4),空间群为Pnma。新相的密度为5.62 g/cm³,比铬铁矿尖晶石密度高9.4%。我们进行了激光加热金刚石砧室实验,以确定铬铁矿尖晶石在12.5 GPa时转变为CF相,然后在高于20 GPa时转变为最近发现的CaTi₂O₄型(CT)结构。由于铬铁矿普遍存在,CF相和CT相可能是地幔岩石、冲击变质的地球岩石和陨石中自然转变序列以及压力和温度条件的重要指示矿物。