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Richardsite, Zn2CuGaS4, A New Gallium-Essential Member of the Stannite Group from the Gem Mines near Merelani, Tanzania
Minerals ( IF 2.5 ) Pub Date : 2020-05-20 , DOI: 10.3390/min10050467
Luca Bindi , John A. Jaszczak

The new mineral richardsite occurs as overgrowths of small (50–400 μm) dark gray, disphenoidal crystals with no evident twinning, but epitaxically oriented on wurtzite–sphalerite crystals from the gem mines near Merelani, Lelatema Mountains, Simanjiro District, Manyara Region, Tanzania. Associated minerals also include graphite, diopside, and Ge,Ga-rich wurtzite. It is brittle, dark gray in color, and has a metallic luster. It appears dark bluish gray in reflected plane-polarized light, and is moderately bireflectant. It is distinctly anisotropic with violet to light-blue rotation tints with crossed polarizers. Reflectance percentages for Rmin and Rmax in air at the respective wavelengths are 23.5, 25.0 (471.1 nm); 27.4, 28.9 (548.3 nm); 28.1, 29.4 (586.6 nm); 27.7, 28.9 (652.3 nm). Richardsite does not show pleochroism, internal reflections, or optical indications of growth zonation. Electron microprobe analyses determine an empirical formula, based on 8 apfu, as (Zn1.975Cu0.995Ga0.995Fe0.025Mn0.010Ge0.005Sn0.005)Σ4.010S3.990, while its simplified formula is (Zn,Cu)2(Cu,Fe,Mn)(Ga,Ge,Sn)S4, and the ideal formula is Zn2CuGaS4. The crystal structure of richardsite was investigated using single-crystal and powder X-ray diffraction. It is tetragonal, with a = 5.3626(2) Å, c = 10.5873(5) Å, V = 304.46(2) Å3, Z = 2, and a calculated density of 4.278 g·cm−3. The four most intense X-ray powder diffraction lines [d in Å (I/I0)] are 3.084 (100); 1.882 (40); 1.989 (20); 1.614 (20). The refined crystal structure (R1 = 0.0284 for 655 reflections) and obtained chemical formula indicate that richardsite is a new member of the stannite group with space group . Its structure consists of a ccp array of sulfur atoms tetrahedrally bonded with metal atoms occupying one-half of the ccp tetrahedral voids. The ordering of the metal atoms leads to a sphalerite(sph)-derivative tetragonal unit-cell, with a » asph and c » 2asph. The packing of S atoms slightly deviates from the ideal, mainly due to the presence of Ga. Using 632.8-nm wavelength laser excitation, the most intense Raman response is a narrow peak at 309 cm−1, with other relatively strong bands at 276, 350, and 366 cm−1, and broader and weaker bands at 172, 676, and 722 cm−1. Richardsite is named in honor of Dr. R. Peter Richards in recognition of his extensive research and writing on topics related to understanding the genesis of the morphology of minerals. Its status as a new mineral and its name have been approved by the Commission of New Minerals, Nomenclature and Classification of the International Mineralogical Association (No. 2019-136).

中文翻译:

理查德斯特(Richardsite),Zn2CuGaS4,坦桑尼亚梅雷拉尼附近宝石矿中锡矿集团新的镓必不可少的成员

新的矿物richardsite是小的(50-400μm)深灰色,呈蝶状晶体的过度生长,没有明显的孪晶,而是外延取向于来自坦桑尼亚曼雅拉地区Simanjiro区Lelatema山的Merelani附近的Merelani宝石矿中的纤锌矿-闪锌矿晶体。 。相关矿物还包括石墨,透辉石和富含锗,镓的纤锌矿。它是易碎的,深灰色的,并具有金属光泽。在反射的平面偏振光下,它看起来是深蓝色,是中等双折射的。它具有各向异性的各向异性,带有偏光镜的紫罗兰色至浅蓝色旋转色。R minR max的反射率在空气中,各自的波长分别为23.5、25.0(471.1 nm);27.4,28.9(548.3 nm); 28.1,29.4(586.6 nm); 27.7、28.9(652.3 nm)。理查德斯特(Richardsite)没有显示多色性,内部反射或生长分区的光学指示。电子探针分析确定的经验式,根据8 apfu,如(锌1.9750.9950.995的Fe 0.0250.0100.005的Sn 0.005Σ4.010小号3.990,而其简化公式是(锌,铜)2(铜, Fe,Mn)(Ga,Ge,Sn)S 4,理想的分子式是Zn 2 CuGaS 4。使用单晶和粉末X射线衍射研究了richardsite的晶体结构。它是四方晶,用一个= 5.3626(2)埃,c ^ = 10.5873(5)A,V = 304.46(2)埃3Ž = 2,且4.278克计算的密度·厘米-3。四个最强的X射线粉末衍射线[ d以Å(I / I 0)为单位]为3.084(100);1.882(40); 1.989(20); 1.614(20)。精细的晶体结构(655次反射,R 1 = 0.0284)和获得的化学公式表明,richardsite是带有空间基团的锡矿组的新成员。它的结构由一个ccp组成与金属原子四面体键合的硫原子阵列,占据了ccp四面体空隙的一半。金属原子引线到闪锌矿的排序(SPH) -衍生物四方晶胞,具有一个»一个SPHç »2一个SPH。S原子的堆积稍微偏离理想状态,主要是由于Ga的存在。使用632.8 nm波长的激光激发,最强烈的拉曼响应是在309 cm -1处的窄峰,在276 cm处有其他相对较强的能带, 350和366 cm -1,以及172、676和722 cm -1的较宽和较弱带。理查德斯特(Richardsite)被任命为纪念彼得·理查兹(R. Peter Richards)博士,以表彰他的广泛研究和有关与理解矿物形态发生有关的主题的文章。其作为新矿物的地位及其名称已得到国际矿物学协会新矿物,命名和分类委员会的批准(第2019-136号)。
更新日期:2020-05-20
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