Study Of Mineralogical Characteristics Of Helvite And Similar Minerals From Huanggangliang,Inner Mongolia

Helvite is a kind of framework silicates containing Mn²⁺,in which Mn²⁺can be easily replaced by Fe²⁺and Zn²⁺to form danalite and genthelvite.In this paper,we studied the chemical composition,spectral characteristics and crystal structure of the helvite samples from Huanggangliang area of Inner Mongolia,and compared with the samples from other places,using large-scale instruments such as electron probe microanalyzer(EPMA),infrared spectrum(IR),Raman,X-ray diffraction(XRD),etc.The helvite from Huanggangliang area of Inner Mongolia has a high degree of idiomorphology and usually in dark red tetrahedral crystal form.It is translucent.The refractive index is 1.66-1.78.It has bright glass luster,and no cleavage.There is no characteristic absorption spectrum.Under ultraviolet fluorescent it is inert.Triangular growth bands can be seen inside.The Mohr's hardness is 7.The helvites are often associated with magnetite,fluorite,quartz and other minerals.The EPMA results demonstrate that the triangular color bands parallel to(111),which is in Hel-01 sample,are caused by the different contents of Fe,Mn and Zn ions in this direction.The reason for the uneven distribution of ions may be the local fluctuation of element content in the surrounding environment during crystallization.The IR spectra show that the characteristic absorption peaks of helvite are 970 cm^-1,923 cm^-1,771 cm^-1,742 cm^-1,706 cm^-1,537 cm^-1,and 413 cm^-1.The Raman characteristic peaks are distributed around 129 cm^-1,142 cm^-1,175 cm^-1,245 cm^-1,296 cm^-1,572 cm^-1,886 cm^-1 and 949cm^-1.XRD powder and single crystal diffraction experiments show that the crystallinity of helvite is high,with cell parameters a=8.2172-8.1490(?).The tetrahedral framework in the helvite is stable and similar to those from other areas,which means the crystal structure of the helvite in Huanggangliang area of Inner Mongolia has no origin identification characteristics.The results of EPMA and Raman demonstrate that Hel-02 is a kind of sulfide,sphalerite,which has similar crystal shape and color.Its chemical formula is Zn_1.01S_1.04,and it's Raman spectra are basically consistent with the standard spectra of sphalerite.