多硅白云母中Fe2+的高压有序效应

21个多硅白云母来自4个低温高压变质带。用电子探针、X射线粉末衍射及穆斯堡尔谱测定其化学成分、b0值及Fe²⁺占位。建立Fe²⁺(M1)/Fe²⁺(M2)对b0值相关图,发现Fe²⁺在八面体晶位有序化并解释其有序机理。     

金绿宝石和变石的呈色机理

对24块世界主要产地的金绿宝石和变石进行X荧光能谱分析,得到其所含的主要微量元素分别是Fe、Ga、Ti和Fe、Cr、Ti。金绿宝石和变石各1块样品的同步辐射X荧光能谱半定量分析表明金绿宝石中Fe含量平均为17 800×10^-6,Cr为855×10^-6;变石中Fe含量为16 060×10^-6,Cr含量达13 333×10^-6。对15个样品的可见吸收光谱进行测试及解释表明金绿宝石的可见吸收光谱是由Fe³⁺引起,变石的可见吸收光谱由Cr³⁺和Fe³⁺共同引起。色度学的分析和系列计算表明具有440～470 nm间最大吸收和540～630 nm宽吸收带的双峰形状的可见吸收光谱,可产生红-绿色的变石效应,通过向着该双峰形状的可见光谱的方向进行变石的优化处理可以获得宝石的变石效应。     

缅甸抹谷Baw-mar矿区蓝宝石的热处理及谱学研究

目前缅甸抹谷矿区开采的蓝宝石原石约80%都要经过优化处理才能投入市场,其中主要为热处理。本文对缅甸抹谷Baw-mar矿区蓝宝石进行不同温度制度的热处理,并利用电子探针、X射线粉晶衍射仪(XRD)、紫外-可见-近红外光谱仪、傅里叶红外光谱仪和激光拉曼光谱仪对其热处理前后的谱学特征进行了对比研究。结果表明,1 300℃热处理后所有样品2θ<60°的XRD衍射峰开始向低角度方向偏移,晶胞参数c/a值随热处理温度升高而降低,推测与其晶体结构在高温下发生畸变有关;Baw-mar矿区蓝宝石的主要致色元素是Fe、Ti和V,其中Fe和Ti共同导致其呈蓝色,V使其略带绿色调,部分样品的灰色调主要由Ni所致;热处理后样品中Fe²⁺-Ti⁴⁺荷移增强,Fe²⁺-Fe³⁺荷移减弱,导致585 nm紫外吸收带增强,746和764 nm吸收峰减弱,同时样品颜色变蓝且灰色调减弱;红外光谱中,样品出现1 988、2 123 cm^-1硬水铝石羟基倍频振动吸收峰和3 619、3 696 cm^-1<...     

滇西兰坪金顶铅锌矿床精细刻画矿化过程：来自硫化物原位微量元素和S-Pb同位素的证据

金顶铅锌矿床位于中国西南中新生代兰坪盆地，是亚洲第二大铅锌矿床，其巨大的储量和复杂的地质成矿史吸引了众多学者的研究，但在矿床成因和矿化过程的精细描述等方面仍存在较大争议。本文通过详细的野外地质调查并结合硫化物的LA-(MC)ICP-MS微量元素和硫、铅同位素分析对该矿床进行了详细解剖。金顶铅锌矿床的含矿地层为景星组砂岩、云龙组含砾砂岩及灰岩角砾岩。成矿过程可分为2个主要阶段：第Ⅰ阶段早期为浸染状的黄铁矿-白铁矿-闪锌矿-方铅矿，晚期硫化物呈块状且出现天青石；第Ⅱ阶段为闪锌矿-方铅矿-黄铁矿-天青石-重晶石-方解石-石膏阶段。成矿过程中硫化物的原位微量元素和S-Pb同位素表现出规律演化特征。主要金属元素除了以简单的类质同象形式赋存于闪锌矿中，Zn²⁺与微量元素存在4Zn²⁺?2Fe²⁺+Ge⁴⁺、2Zn²⁺?Fe²⁺+Mn²⁺、3Zn²⁺?In³⁺+Sn³⁺等复杂的替代关...     

白云母-金红石质图章石的矿物学特征

绿色图章石是我国众多图章石品种中的重要类别，四川“雅安绿”即为其中一个代表性的品种。近期国内珠宝市场出现了一种被称为“雅安绿”新亚种的图章石且广受关注，其外观为微透明的绿黄色基体上分布绿色半透明的纹脉，图案精美。本次研究采用偏光显微镜、X射线粉末衍射仪、电子探针仪、红外吸收光谱仪、激光拉曼光谱仪和紫外-可见光分光光度计对该种图章石的矿物组成、化学成分、谱学特征和颜色成因进行研究。结果表明，该图章石绿色纹脉的主要矿物成分为微晶白云母，绿黄色基体主要由微晶白云母和金红石组成，纹脉白云母中可充填有细脉状的绿泥石。明确了该图章石中白云母的多型类型为2M₁型，白云母的晶胞参数为a=0.514(2) nm、b=0.906(4) nm、c=2.015(6) nm、β=95.3(3)°,金红石的晶胞参数为a=b=0.460(2) nm、c=0.295(1) nm,计算其分子式为(K_0.82Na_0.08)(Al_1.80Fe_0.17Mg_0.03)(Al_0.93     

鄂尔多斯盆地南部旬邑-宜君地区直罗组古层间氧化带地球化学特征及水-岩作用探讨

鄂尔多斯盆地南部旬邑-宜君地区直罗组古层间氧化带具有明显分带特征,通过对不同分带砂岩主量、微量、稀土元素及环境敏感参数特征对比研究,将旬邑-宜君地区古层间氧化带发育的水-岩作用过程划分成两个阶段：古层间氧化带形成和大规模成矿阶段、二次还原改造阶段。(1)古层间氧化带形成和大规模成矿阶段：含氧水进入目的层砂体,使砂体中Fe²⁺氧化成Fe³⁺(Fe²⁺含量最低,Fe³⁺最高);砂体中的U被氧化为U⁶⁺,形成铀酰腐殖酸盐络合物发生迁移(U、Corg、S含量最低、Th/U比值最高);长石高岭土化使Si发生流失(SiO₂含量降低);携带大量U的氧化流体运移至氧化还原过渡带(Corg、∑S含量最高、Fe²⁺含量仅低于灰绿色砂体),还原剂(有机质和黄铁矿等)将U⁶⁺还原成U⁴⁺,形成沥青铀矿;U⁴⁺与SiO₄^4-发生反应形成铀石(Th/U比...     

松辽盆地红岗油田白垩系青山口组含片钠铝石砂岩自生矿物共生序列

松辽盆地红岗油田白垩系青山口组发育含片钠铝石砂岩。通过偏光显微镜、扫描电镜、阴极发光 仪、Ｘ射线衍射等多种技术手段,对含片钠铝石砂岩的碎屑成分、胶结物类型及自生矿物共生序列等特征进行 了研究。该区含片钠铝石砂岩为岩屑长石砂岩及长石岩屑砂岩,胶结物有次生加大长石、次生加大石英、自生 石英微晶、黏土矿物、片钠铝石、方解石、铁方解石及铁白云石。方解石的形成分为两期,第１期方解石为原 始生物碎屑颗粒溶蚀溶解的产物,第２期方解石可能与ＣＯ^２ 充注后钙长石及早期碳酸盐矿物的溶蚀溶解有关。 含片钠铝石砂岩的自生矿物共生序列为：次生加大长石、早期次生加大石英-自生石英微晶-早期高岭石、第１ 期方解石、片钠铝石-晚期次生加大石英-晚期高岭石、第２期方解石、铁方解石、铁白云石。其中ＣＯ^２ 注入 后的矿物共生组合为：片钠铝石-晚期次生加大石英-晚期高岭石、第２期方解石、铁方解石、铁白云石。     

陕西商洛紫绿玛瑙的宝石学特征及致色机理研究

通过常规宝石学仪器、偏光显微镜、电子探针及扫描电子显微镜等检测手段,对陕西商洛紫绿玛瑙的宝石学特征及致色机理进行了深入研究。研究表明,紫绿玛瑙是典型的石英质玉石,颜色以绿色、紫红色为主,颜色分布多以紫心绿边、灰白心绿边、淡青白色加紫红色等纹带特征出现,半透明—微透明,部分透明度较好的区域可见明显包裹体。紫绿玛瑙为典型的隐晶质结构,主要组成矿物为石英,结晶程度较好,为呈半自形—他形结构,含量≥90%,粒径为1~25μm,分布均匀;次要矿物有绿泥石、绢云母、铁白云石、白云石等。紫绿玛瑙为矿物致色,紫红色的致色矿物为铁的氧化物或氢氧化物,粒度微细,粒径为1~10μm,呈星点状均匀分布,含量为1%~2%;绿色的致色矿物为绿泥石,含量较高(6%~7%),主要呈集合体状均匀的分布于石英粒间,绿泥石含量与绿色区域的颜色深浅程度成正比。     

华北中元古代鱼骨状方解石: 成因机制和古环境意义*

鱼骨状方解石是一种特殊的碳酸盐沉积,由锯齿状亮暗交互的亚毫米级条带组成,主要见于太古宙。以往认为,鱼骨状方解石属无机化学沉淀成因,形成于水体缺氧、碳酸盐过饱和、富Fe²⁺、Mn²⁺等碳酸盐沉淀抑制剂的环境条件;在地质记录中其丰度随时间的减少反映了海洋的长期氧化趋势。文中首次在华北地台中元古界高于庄组四段微生物礁内发现了大量鱼骨状方解石。宏观观察表明,这些鱼骨状方解石主要以微生物礁孔洞充填物形式产出,明显区别于太古宙以海底沉淀形式直接产出在海底的鱼骨状方解石。显微研究发现,鱼骨状方解石晶体纤维具有沿晶体生长方向旋转消光特征,证明其内部亚晶的光学C轴从纤维底部的随机排列逐步旋转至上部垂直纤维生长方向。这符合球状晶体生长模式,需要方解石沉淀抑制剂的参与。鱼骨状方解石产出具有丰度随时间减少以及产出形式由海底沉淀向孔洞胶结物转变的特征。这些特征与海洋氧化逐渐增强以及具氧化还原敏感属性的碳酸盐沉淀抑制剂逐渐从水体中移除相吻合。笔者认为鱼骨状方解石的沉淀抑制剂为Fe²⁺和Mn²⁺,这与微生物岩无明显Ce异常和Fe²⁺极强的抑制能力相一致。因此,鱼骨状方解石可用于指示缺氧环境条件。此外,显微和超微研究也表明鱼骨状方解石晶体内存在有大量与其生长方向一致的菌丝体残余和与之密切伴生的有机矿物,表明微生物为鱼骨状方解石成核和初始沉淀提供了重要垫板。     

碧石的宝石学分类及定义界定初探

碧石属于石英质玉中一类,少有文献对其深入探讨,缺乏系统性分类以及定义界定,不能准确区别于颜色相对应的玉髓(玛瑙).为解决上述问题,本次研究应用X射线衍射、拉曼光谱、红外光谱、电子探针、紫外—可见光光谱等多种测试技术相结合方式,初步确定常见单色碧石的致色矿物,其中红碧石的致色矿物为赤铁矿,黄碧石的致色矿物为针铁矿,绿碧石的致色矿物为绿鳞石,紫碧石的致色矿物是锐钛矿和赤铁矿.结合市场实际需求,从宝石学角度以颜色特征作为碧石分类依据,将碧石从宝石学分类角度,分为红碧石、黄碧石、绿碧石、紫碧石、血滴石、风景碧石、多彩碧石等七个大类.同时,根据X射线衍射半定量分析和电子探针测试近似计算结果:红碧石测试样品中赤铁矿平均含量均不低于2.187％,凉山南红样品红色富集区域测试赤铁矿含量不高于1.767％,低于2％.因此可以考虑将2％的赤铁矿含量作为区别红碧石和南红的界限.建议以杂质矿物含量2％对碧石和相似颜色的玉髓(玛瑙)区分界定,进一步补充完善已有碧石定义.     

Natural iron-containing blue and colorless euclase studied by electron paramagnetic resonance

Natural blue and colorless rare-gem mineral specimens of euclase from Brazil are investigated by electron paramagnetic resonance (EPR). Angular dependences of Fe³⁺ EPR spectra in three mutually perpendicular crystal planes are analyzed revealing g and D tensors with significant low-symmetry effects, as for example, the high asymmetry parameter E/D = 0.28. Fourth-order degree Stevens parameters are also included in analysis. The anisotropy of both g and D tensors is consistent with Fe³⁺ substituting for Al³⁺ ions in strongly distorted AlO₅(OH) octahedra in which the oxygen distances range from 1.85 to 1.98 Å. Fe³⁺ is not responsible for the blue color because colorless and blue euclase show nearly the same Fe³⁺ concentration as measured by EPR. However, total iron content in blue sample is much higher than in the colorless one suggesting that the existing model that Fe²⁺–Fe³⁺ intervalence charge transfer transition may explain the blue color of euclase.     

Celadonite mica: Solid solution and stability

Phase relations for the bulk compositions of the celadonites between the MgAl, MgFe³⁺ and Fe²⁺Fe³⁺ types (celadonite = KR²⁺R³⁺ Si₄O₁₀ (OH)₂) under magnetite-iron and nickel-nickel oxide solid-fluid buffers indicate the extent of solid solution possible in this potassic mica series at temperatures between 300° and 430° C at 2 Kb total pressure. Other possible combinations of Mg, Al, Fe ions in octahedrally coordinated sites did not produce single-phase mica products. The ferrous celadonite micas are stable only under oxygen fugacities where magnetite is the stable oxide—where both Fe²⁺ and Fe³⁺ can coexist. However the celadonite with the highest thermal stability at 2 Kb total pressure, nickel-nickel oxide buffer conditions is the KMgFe³⁺Si₄O₁₀(OH)₂ phase which is stable up to 420°C, well into low grade metamorphic conditions. It is thus apparent that the presence of celadonite or glauconite mica will not be indicative of changing diagenetic conditions.     

Energy transfer among Pb, Ce and Mn in fluorescent calcite from Kuerle, Xinjiang, China

Natural calcite from Kuerle, Xinjiang, China, shows orange-red fluorescence when exposed to short-wave ultraviolet (UV) light (Hg 253.7 nm). Photoluminescence (PL) emission and excitation spectra of the calcite are observed at room temperature in detail. The PL emission spectrum under 208 nm excitation consists of three bands: two UV bands at 325 and 355 nm and an orange-red band at 620 nm. The three bands are ascribed to Pb²⁺, Ce³⁺ and Mn²⁺, respectively, as activators. The Pb²⁺ excitation band is observed at 243 nm, and the Ce³⁺ excitation band at 295 nm. The Pb²⁺ excitation band is also observed by monitoring the Ce³⁺ fluorescence, and the Pb²⁺ and Ce³⁺ excitation bands, in addition to six Mn²⁺ excitation bands, are also observed by monitoring the Mn²⁺ fluorescence. These indicate that four types of the energy transfer can occur in calcite through the following processes: (1) Pb²⁺ → Ce³⁺, (2) Pb²⁺ → Mn²⁺, (3) Ce³⁺ → Mn²⁺ and (4) Pb²⁺ → Ce³⁺ → Mn²⁺.     

Biotite and garnet compositional variation and mineral equilibria in Grenville gneisses of the Otter Lake area, Quebec

Garnet-biotite gneisses, some of which contain sillimanite or hornblende, are widespread within the Otter Lake terrain, a portion of the Grenville Province of the Canadian Shield. The metamorphic grade is upper amphibolite to, locally, lower granulite facies. The atomic ratio Fe²⁺/(Fe²⁺+ Fe³⁺) in biotite ranges from 0.79 to 0.89 (ferrous iron determinations in 10 highly pure separates), with a mean of 0.86. Mg and Fe²⁺ atoms occupy 67–78% of the octahedral sites, the remainder are occupied by Fe³⁺, Ti, and Al, and some are vacant. Mg/(Mg + Fe²⁺), denoted X, in the analysed samples ranges from 0.32 to 0.65. Garnet contains 1–24% grossular, 1–12% spessartine and X ranges from 0.07 to 0.34. Compositional variation in biotite and garnet is examined in relation to three mineral equilibria: (I) biotite + sillimanite + quartz = garnet + K-feldspar + H₂O; (II) pyrope + annite = almandine + phlogopite; (III) anorthite = grossular + sillimanite + quartz. Measurements of X (biotite) and X (garnet) are used to construct an illustrative model for equilibrium (I) which relates the observed variation in X to a temperature range of 70°C or a range in H₂O activity of 0.6; the latter interpretation is preferred. In sillimanite-free gneisses, the distribution of Mg and Fe²⁺ between garnet (low in Ca and Mn) and biotite is adequately described by a distribution coefficient (KD) of 4.1 (equilibrium II). The observed increase in the distribution coefficient with increasing Ca in garnet is ln K_D= 1.3 + 2.5 × 10^?2 [Ca] where [Ca] = 100 Ca/(Mg + Fe²⁺+ Mn + Ca). The distribution coefficient is apparently unaffected by the presence of up to 12% spessartine in garnet. In several specimens of garnet-sillimanite-plagioclase gneiss, the Ca contents of garnet and of plagioclase increase in unison, as required by equilibrium (III). The mean pressure calculated from these data (n= 17) is 5.9 kbar, and the 95% confidence limits are ±0.5 kbar.     

Chromium and vanadium impurities in natural green euclase and their relation to the color

Natural specimens of green gemological euclase (chemical formula BeAlSiO₄(OH)) from Brazil were investigated by electron paramagnetic resonance (EPR) and optical absorption. In addition to iron-related EPR spectra, analyzed recently in blue and colorless euclase, chromium and vanadium-related EPR spectra were also detected in green euclase. Their role as color causing centers is discussed. The results indicate that Cr³⁺ ions substitute for Al³⁺ ions in the euclase structure. The EPR rotation patterns of Cr³⁺ with electron spin S = 3/2 were analyzed with monoclinic spin Hamiltonian leading to the parameters of g _xx , g _yy and g _zz equal to 2.018, 2.001 and 1.956 and electronic fine structure parameters of D = −8.27 GHz and E = 1.11 GHz, respectively, with high asymmetry ratio E/D = 0.13. For the vanadium-related EPR spectra the situation is different. It is concluded that vanadium is incorporated as the vanadyl radical VO²⁺ with electron spin S = 1/2 with nearly axial spin Hamiltonian parameters g_zz = 1.9447, g _xx  = 1.9740 g _yy  = 1.9669 and axial hyperfine interactions due to the nuclear spin I = 7/2 of the ⁵¹V isotope leading to A _zz  = 502 MHz, A _xx  = 150 MHz and A _yy  = 163 MHz. The green color of euclase is caused by two strong broad absorption bands centered at 17,185 and 24,345 cm⁻¹ which are attributed to the ⁴A_2g → ⁴T_2g, ⁴T_1g transitions of Cr³⁺, respectively. Vanadyl radicals may introduce some absorption bands centered in the near infrared with tail extending into the visible spectral range.     

Structure and physical property relations of Mn ilvaite

Structural and compositional data as well as ⁵⁷Fe Mössbauer parameters were determined on a natural Mn-rich monoclinic ilvaite crystal (ideal composition CaFe ₂ ²⁺ Fe³⁺Si₂O₈(OH)) which was used for electrical conductivity and thermopower measurements (part 2 of this paper). A zonar structure was found by electron microprobe analysis with a strong decrease in Mn concentration from the rim to the centre of the crystal in a plane perpendicular to the [001] direction. X-ray powder diffraction analysis of the most Mn-rich composition was performed. Mn²⁺ cations populate preferentially M2 sites of the ilvaite unit cell (space group P21/a), to a lower extent they reside on M1 and a reduced part is on Ca sites. The monoclinic angle was determined to β=90.178(4)°. The structural results are compared to literature data for other natural Mn-rich as well as low-impurity ilvaites; this concerns in particular the lattice b parameter and the undecided issue of the varying β angle. In the literature, the order parameter σ, which describes the varying degree of ordering of Fe²⁺–Fe³⁺ pairs on M11 and M12 sites in chains running parallel to the [001] direction, and structural defects are thought to be related to β. The interrelationship between β and σ with respect to a possible twin domain structure is discussed. Various ⁵⁷Fe Mössbauer spectra were recorded between 151 K and 327 K. Mössbauer parameters and Fe²⁺/Fe³⁺ concentration ratios were determined from the fits to the spectra. Fitting of subspectra was accomplished with the idea to find assignments of Fe²⁺ and Fe³⁺ doublets in agreement with X-ray results. The fraction of Mn²⁺ substituting Fe²⁺ on M1 sites could be estimated.     

河北宽城蛇纹石玉的宝石矿物学特征研究

河北宽城蛇纹石玉结构细腻,颜色可呈肉红色、绿色,当地市场称之为"热河玉"。本文通过常规宝石学测试结合激光拉曼光谱、电子探针、X射线粉晶衍射、激光剥蚀等离子质谱以及可见光吸收光谱等手段对其进行了系统分析,并采用伽玛能谱仪对其放射安全性进行了检测。结果表明,肉红色样品折射率及相对密度值均较低,折射率为1.54~1.55,相对密度为2.33~2.43,主要组成矿物为斜纤蛇纹石,主要具纤维交织结构、纤维柱粒交织结构,局部可见变余生物骨架结构,次要矿物有方解石和透辉石,Fe和Mn元素含量相对较高,Fe元素含量范围在184.9×10^-6~951.7×10^-6,Mn元素含量为106.4×10^-6~287.3×10^-6;绿色样品折射率为1.55~1.56,相对密度为2.58~2.62,主要组成矿物为叶蛇纹石,具更加细腻的纤维交织结构,次要矿物为滑石及四方硫铁矿,Fe元素含量极高,可达5 979×10^-6~6 359×10^-6。结合可见光吸收光谱分析结果认为Fe³⁺、Fe²⁺以及Mn³⁺的综合作用是导致样品呈现肉红色的主要原因,而Fe²⁺和Fe³⁺则是导致绿色的主要原因。放射性检测结果显示样品的内、外照射指数及放射性比活度值均低于标准要求,对人体无放射性危害。