【摘要】 1982年笔者在河北符山矿镁矽卡岩的裂隙中发现了碳硅钙石,具完好的板状晶体,发育有{100},{101},{120},{201}等单形。Ng=1.628,Nm=1.615,Np=1.609,（+）2V=67°;比重为2.76;空间群I2/m;a_o=10.1206,b_o=15.2058,c_o=6.6345;β=100°37′;Z=2.结构式为(Ca_7.03Fe_0.01Mn_0.01K_0.002)〔Si₆O₁₈〕_0.98（CO₃）₁.06·2.1 H₂O,主要X—射线衍射线为3.02（100）,2.99（80）,2.78（35）,2.49（40）,1.896（40）。红外光谱有21个吸收带,CO₃群的伸缩振动谱带有明显分裂。DTA曲线表现有240℃及757℃两个吸热谷及895℃的放热峰。该地产出的碳硅钙石是矽卡岩晚期的低温热液矿物,与方解石,钙沸石,雪硅钙石,吉水硅钙石和硅灰石产膏等共生。更多还原

【Abstract】 Scawtite, a rare carbonated calcium silicate hydrate mineral, was discovered at the Fushan mine, Hebei Province in 1982. It occurs in cavities of the magnesian skarn near the contact zone, coexisting with calcite, scolecite, tobermorite, gyrolite and thaumasite. Its colorless and transparent crystals look like rectangular tablets with such forms as{100}, {010}, {101},{120}, {201}, {301}, {211},{311} and {611}. Its optical constants are Ng=1. 629, Nm=1. 615, Np=1. 609, （+）2V = 67°, c∧Ng=30～35°, and its specific gravity is 2.76.The structural parameters, determined on a Nicolet-R3 four-circle diffractometer, are as follows: space group I2/m, a_o=10. 1206, b_o=15. 2058, c_o = 6.6345, β=100°37’and Z=2. The data obtained from microprobe analysis and loss in weight on ignition give a structural formula of (Ca_7.03Fe_0.01Mn_0.01K_0.002) [Si₆O₁₈]_0.98 [CO₃]_1.06·2.1H₂O.X-ray diffraction shows the spacings and intensities of the five stronger lines to be 3.02（100）, 2.99（80）, 2.78（35）, 2.49（40）, and 1.896（40） respectively.There are 21 absorption bands in the infrared spectra corresponding with the structure of scawtite. The stretch vibration of the CO₃ group splits into two bands with wavenumber being 1486 and 1448cm^-1 respectively. The explanation is that the CO₃ triangles are horizontal isosceles ones with the length of one C-O bond different from that of the other two C-O bonds, thus reducing the symmetry from D_3h to C_2h and resulting in the disappearance of the degeneration and the split of the absorption band.The DTA curve shows two endothermic troughs at 240℃ and 757℃ and an exothermic crest at 895℃, resulting respectively from loss of crystallization water, escape of CO₂ and formation of wollastonite as a new phase.Scawtite is a typical low-temperature hydrothermal mineral formed at about 100℃.更多还原