Abundant TiO2-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 TiO2-II.Irregular thin layered TiO2-Ⅱ is also observed in coarse-grained rutile fragments,where the TiO2-Ⅱ layers distributes along fractures and cracks in rutile.About 30 percent of rutile in the gneiss had been transformed to TiO2-Ⅱ.Fine grains of TiO2-Ⅱ display light bluish grey to light yellow brown in plane-polarized reflected light.Crystallographic investigation shows that TiO2-Ⅱ has an orthorhombic structure with space group Pbcn.The cell parameters are a=4.543(1),b=5.491(9)and c=4.895(2).Its empirical formula calculated on the basis of two oxygen atoms can be written as(Ti0.985Fe0.008Nb0.006-Si0.003Zr0.001)1.003O2,or simply formula TiO2.According to the shock effects of quartz and feldspars,the peak shock pressure and post-shock temperature in the TiO2-Ⅱ-bearing gneiss are estimated to be between 35 and 43 GPa and 300–900°C,respectively.The finding of TiO2-Ⅱ in the shock-metamorphosed gneiss provides another mineral physics evidence for shock origin of the Xiuyan crater. Abundant TiO2-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 TiO2-II. Irregularly thin layered TiO2-II is also observed in coarse-grained rutile fragments, where the TiO2-II layers distributes along fractures and cracks in rutile. About 30 percent of rutile in the gneiss had been transformed to TiO2- II. Fine grains of TiO2-II display light bluish gray to light yellow brown in plane-reflected reflected light. Crystallographic investigation shows that TiO2-II has an orthorhombic structure with space group Pbcn. The cell parameters are a = 4.543 (1), b = 5.491 (9) and c = 4.895 (2) .Its empirical formula calculated on the basis of two oxygen atoms can written as (Ti0.985Fe0.008Nb0.006- Si0.003Zr0.001) 1.003O2, or simply formula TiO2. According to the shock effects of quartz and feldspars, the peak shock pre ssure and post-shock temperature in the TiO2-II-bearing gneiss are estimated to be between 35 and 43 GPa and 300-900 ° C, respectively. The finding of TiO2-II in the shock-metamorphosed gneiss provides another mineral physics evidence for shock origin of the Xiuyan crater.