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青川石英质玉是近年在四川省发现的新玉石矿。玉石矿体赋存于新元古界通木梁群太阳坪组云母石英片岩中。玉石的矿物成分主要为石英、铬云母、铬绢云母,具显微细粒粒状、片状变晶结构,片状、条带状构造。玉石种类分为绿色和白绿色,具油脂光泽;矿体规模大、块度好,玉石品质佳、可加工性强,可制作手镯、摆件、挂件、雕件等。根据野外地质工作判断,青川石英质玉属于区域变质成因,青川玉石矿的发现填补了四川石英质玉的空白,对丰富区域成矿系列和拓展区域玉石矿找矿方向具有重要意义。 相似文献
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常宁玉是产于湖南省常宁县的一种玉石新品种,属透辉石质玉,玉石结构均匀,细腻,光泽好,硬度较大,可加工减雕刻成多种多样的工艺品。 相似文献
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石英岩质玉是一种市场上常见且产地较多的玉石品种,本文基于前人石英岩质玉的研究基础,通过常规宝石学测试、红外光谱测试、偏反光显微镜下观察,以及采用X射线粉晶衍射、X射线荧光光谱、电感耦合等离子体质谱仪对样品的宝石学特征、矿物组成进行分析,并对其成因进行讨论。结果表明:该地区黑色石英岩质玉多为中-细粒粒状结构,偏光显微镜观察可见多种变晶/变余结构;成分中主要矿物石英平均含量为44.7%,次要矿物云母、长石平均含量合计31.0%,黏土矿物平均含量为12.7%,另含有有机碳以及红柱石、铁铝榴石、黄铁矿等铁质矿物;结合样品结构、构造特征及矿物化学成分分析可知,样品为典型副变质岩系的中、低温热液交代型区域变质岩,属绿片岩相,原岩为富铝且富含石英、长石的沉积岩,其形成的构造环境属大陆边缘构造。本研究为该地区石英岩质玉的矿物组成鉴定提供了多手段技术支撑。 相似文献
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红宝石和蓝宝石因其色美、透明,早在古代,人们化视为吉祥之物。它们曾与钻石、珍珠一起成为英帝国国王、俄国沙皇皇冠和礼服上不可缺少的饰物。自从近百年来珠宝玉石进入民间以来,红宝石、蓝宝石与钻石、祖母绿、金绿宝石被公认为世界五大名贵宝石,是人们十分宠爱的宝石品种。红宝石和蓝宝石同是一种矿物——刚玉,化学成分均为Al2O3。纯净的Al2O3是无色的,只因含有不同的微量元素,才使刚玉类宝石变得五光十色、绚丽多彩。红宝石中含有Cr而呈现红色,蓝宝石含有Ti和Fe而显蓝色。现将红宝石和蓝宝石的鉴定特征及其评价分叙如下。1红… 相似文献
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李林安 《青海地质科技情报》1996,(1):16-22
青海省与基性-超基性岩有关的玉石矿,主要包括两类;钙铝榴石质玉和蛇纹石质玉。根据笔者的调查,以及有关的信息资料,本文着重对钙铝榴石质玉的基本特征作一介绍。 相似文献
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应用同步辐射技术解析黄色-红色石英质玉石中的致色矿物 总被引:1,自引:1,他引:0
质地细腻、颜色多彩的隐晶质-微粒脉石英在我国珠宝行业称为石英质玉石,颜色是石英质玉石价值判断的主要因素之一,揭示其致色矿物及致色机理对于研究石英质玉石的颜色评价指标和矿床成因具有重要意义,但前人并未直接获得致色矿物的准确信息。本文运用上海光源(SSRF)BL15U1线站的同步辐射硬X射线,使用μ-XRF和μ-XRD技术对黄色和红色隐晶质-微粒脉石英中的致色矿物进行了研究。结果表明,黄色石英质玉石由赋存于石英颗粒间或微裂纹中的针铁矿(特征衍射峰0.49574、0.41594、0.26887、0.25705、0.25189、0.24510、0.21806、0.17133 nm)或其集合体致色,红色石英质玉石由赋存于石英颗粒间或微裂纹中的赤铁矿(特征衍射峰0.36774、0.27091、0.25200 nm)或其集合体致色,黄色-红色石英质玉的颜色由针铁矿和赤铁矿共同致色,赤铁矿的显色能力要高于针铁矿。本文获得了石英质玉石中致色矿物的直接数据,为玉石结晶温度与致色机理的探讨、石英质玉石的品质评价提供了依据。 相似文献
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Corundum (ruby-sapphire) is known to have formed in situ within Archean metamorphic rocks at several localities in the North Atlantic Craton of Greenland. Here we present two case studies for such occurrences: (1) Maniitsoq region (Kangerdluarssuk), where kyanite paragneiss hosts ruby corundum, and (2) Nuuk region (Storø), where sillimanite gneiss hosts ruby corundum. At both occurrences, ultramafic rocks (amphibole-peridotite) are in direct contact with the ruby-bearing zones, which have been transformed to mica schist by metasomatic reactions. The bulk-rock geochemistry of the ruby-bearing rocks is consistent with significant depletion of SiO2 in combination with addition of Al2O3, MgO, K2O, Th and Sr relative to an assumed aluminous precursor metapelite. Phase equilibria modelling supports ruby genesis from the breakdown of sillimanite and kyanite at elevated temperatures due to the removal of SiO2. The juxtaposition of relatively silica- and aluminum-rich metasedimentary rocks with low silica ultramafic rocks established a chemical potential gradient that leached/mobilized SiO2 allowing corundum to stabilize in the former rocks. Furthermore, addition of Al2O3 via a metasomatic reaction is required, because Al/Ti is fractionated between the aluminous precursor metapelites and the resulting corundum-bearing mica schist. We propose that Al was mobilized either by complexation with hydroxide at alkaline conditions, or that Al was transported as K-Al-Si-O polymers at deep crustal levels. The three main exploration vectors for corundum within Archean greenstone belts are: (1) amphibolite- to granulite-facies metamorphic conditions, (2) the juxtaposition of ultramafic rocks and aluminous metapelite, and (3) mica-rich reactions zones at their interface. 相似文献
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苏北榴辉岩经历了5期以上变质变形作用,其中至少有两期高压或超高压变质变形作用。其pTt轨迹呈顺时针方向旋转。榴辉岩形成后,随着地体的反弹、推覆,于印支期末迅速回返到中地壳,再经燕山期-喜山期区域隆升和拉伸折返,最终剥露于现代侵蚀面。苏胶造山带至少经历了晋宁期、印支期和燕山期三次造陆或造山运动。苏北榴辉岩等的成矿组合为金红石、蓝晶石、金刚石、石榴红宝石及水晶等。 相似文献
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Tomoki Taguchi Yohei Igami Akira Miyake Masaki Enami 《Journal of Metamorphic Geology》2019,37(3):401-414
To understand the preservation of coesite inclusions in ultrahigh‐pressure (UHP) metamorphic rocks, an integrated petrological, Raman spectroscopic and focussed ion beam (FIB) system–transmission electron microscope (TEM) study was performed on a UHP kyanite eclogite from the Sulu belt in eastern China. Coesite grains have been observed only as rare inclusions in kyanite from the outer segment of garnet and in the matrix. Raman mapping analysis shows that a coesite inclusion in kyanite from the garnet rim records an anisotropic residual stress and retains a maximum residual pressure of ~0.35 GPa. TEM observations show quartz is absent from the coesite inclusion–host kyanite grain boundaries. Numerous dislocations and sub‐grain boundaries are present in the kyanite, but dislocations are not confirmed in the coesite. In particular, dislocations concentrate in the kyanite adjacent to the boundary with the coesite inclusion, and they form a dislocation concentration zone with a dislocation density of ~109 cm?2. A high‐resolution TEM image and a fast Fourier transform‐filtered image reveal that a tiny dislocation in the dislocation concentration zone is composed of multiple edge dislocations. The estimated dislocation density in most of the kyanite away from the coesite inclusion–host kyanite grain boundaries is ~108 cm?2, being lower than that in kyanite adjacent to the coesite. In the case of a coesite inclusion in a matrix kyanite, using Raman and TEM analyses, we could not identify any quartz at the grain boundaries. Dislocations are not observed in the coesite, but numerous dislocations and stacking faults are developed in the kyanite. The estimated overall dislocation density in the coesite‐bearing matrix kyanite is ~108 cm?2, but a high dislocation density region of ~109 cm?2 is also present near the coesite inclusion–host kyanite grain boundaries. Inclusion and matrix kyanite grains with no coesite have dislocation densities of ≤108 cm?2. Dislocation density is generally reduced during an annealing process, but our results show that not all dislocations in the kyanite have recovered uniformly during exhumation of the UHP rocks. Hence, one of the key factors acting as a buffer to inhibit the coesite to quartz transformation is the mechanical interaction between the host and the inclusion that lead to the formation of dislocations in the kyanite. The kyanite acts as an excellent pressure container that can preserve coesite during the decompression of rocks from UHP conditions. The search for and study of inclusions in kyanite may be a more suitable approach for tracing the spatial distribution of UHP metamorphic rocks. 相似文献
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Kinetic control of staurolite–Al2SiO5 mineral assemblages: Implications for Barrovian and Buchan metamorphism 下载免费PDF全文
The distribution and textural features of staurolite–Al2SiO5 mineral assemblages do not agree with predictions of current equilibrium phase diagrams. In contrast to abundant examples of Barrovian staurolite–kyanite–sillimanite sequences and Buchan‐type staurolite–andalusite–sillimanite sequences, there are few examples of staurolite–sillimanite sequences with neither kyanite nor andalusite anywhere in the sequence, despite the wide (~2.5 kbar) pressure interval in which they are predicted. Textural features of staurolite–kyanite or staurolite–andalusite mineral assemblages commonly imply no reaction relationship between the two minerals, at odds with the predicted first development (in a prograde sense) of kyanite or andalusite at the expense of staurolite in current phase diagrams. In a number of prograde sequences, the incoming of staurolite and either kyanite, in Barrovian sequences, or andalusite, in Buchan‐type sequences, is coincident or nearly so, rather than kyanite or andalusite developing upgrade of a significant staurolite zone as predicted. The width of zones of coexisting staurolite and either kyanite, in Barrovian sequences, or andalusite, in Buchan‐type sequences, is much wider than predicted in equilibrium phase diagrams, and staurolite commonly persists upgrade until its demise in the sillimanite zone. We argue that disequilibrium processes provide the best explanation for these mismatches. We suggest that kyanite (or andalusite) may develop independently and approximately contemporaneously with staurolite by metastable chlorite‐consuming reactions that occur at lower P–T conditions than the thermodynamically predicted staurolite‐to‐kyanite/andalusite reaction, a process that involves only modest overstepping (<15°C) of the stable chlorite‐to‐staurolite reaction and which is favoured, in the case of kyanite, by advantageous nucleation kinetics. If so, the pressure difference between Barrovian kyanite‐bearing sequences and Buchan andalusite‐bearing sequences could be ~1 kbar or less, in better agreement with the natural record. The unusual width of coexistence of staurolite and Al2SiO5 minerals, in particular kyanite and andalusite, can be accounted for by a combination of lack of thermodynamic driving force for conversion of staurolite to kyanite or andalusite, sluggish dissolution of staurolite, and possibly the absence of a fluid phase to catalyse reaction. This study represents an example of how kinetic controls on metamorphic mineral assemblage development have to be considered in regional as well as contact metamorphism. 相似文献
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"广东绿"玉石矿床发育于广东省广宁县五指山地区.玉石矿脉的空间分布受岩性控制,赋存于花岗闪长斑岩或花岗斑岩中;玉石原石色彩多样,岩石以显微鳞片变晶结构和块状构造为主;矿区围岩蚀变发育,具有绢云母化、高岭土化和黄铁矿化的蚀变分带现象.矿物学分析表明,"广东绿"是一种特殊的云母质玉石,主要由绢云母和水白云母组成,其全岩地球化学特征和云母的矿物化学组成相一致.成矿作用分析表明,晚期侵入的岩浆岩脉、剪切断裂带和中低温酸性流体活动构成了玉石矿形成的主要地质条件.研究认为 "广东绿"玉石是一种特殊的绢云英岩化产物,即花岗质岩石遭受岩浆期后浅成中低温热水溶液蚀变和强烈的水化作用而成. 相似文献
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Cathodoluminescence (CL) mapping of kyanite in high pressure, aluminous granulites from the central Grenville Province reveals internal structures that are linked to their metamorphic reaction history. In two samples, individual kyanite crystals are shown to be composite porphyroblasts comprising three distinct generations, defined by their CL intensity and Cr (±V, Ti, Fe and Ga) content, and each separated by resorbed interfaces. In contrast, a sub‐aluminous sample contains two types of kyanite, one as resorbed inclusions in garnet and another in the groundmass or replacing garnet. These textural variants of kyanite are interpreted within the framework of phase equilibria modelling. In P–T pseudosections, a first generation of kyanite, which is only present in the most aluminous samples, is potentially linked to staurolite breakdown, and its resorption is consistent with a subsequent increase in pressure. This kyanite represents the earliest remnant of prograde metamorphism identifiable in these rocks. The second generation, present in the porphyroblasts in the same samples and as inclusions in garnet in the sub‐aluminous sample, is interpreted to be the peritectic product of muscovite dehydration melting. Resorption of this kyanite is consistent with subsequent continuous dehydration melting of biotite, which is also inferred based on microstructural considerations. The final generation of kyanite, present as rims on the prograde kyanite porphyroblasts in aluminous samples and as part of the groundmass or replacing garnet in the sub‐aluminous rock, is interpreted to have grown during melt crystallization upon retrogression. The presence of retrograde kyanite implies that the melt crystallized over a wide range of temperatures, and provides an important constraint on the P–T conditions of the metamorphic peak and on the retrograde P–T path. CL mapping is crucial for identifying retrograde kyanite in aluminous samples, as it preferentially overgrows existing kyanite rather than replacing other prograde phases. The scarcity of kyanite in sub‐aluminous rocks allows retrograde kyanite to grow as discrete crystals that can be identified by optical microscopy. This work attests to the potential of unconventional tools such as CL imaging for deciphering the metamorphic history of rocks. 相似文献
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和田玉、玛纳斯碧玉和岫岩老玉的产地特征 总被引:7,自引:2,他引:7
本文用电子探针研究了和田玉、玛纳斯碧玉和岫岩老玉的矿物成分,结果表明和田玉的主要矿物成分是透闪石,玛纳斯碧玉是阳起石,而岫岩老玉则由透闪石和阳起石组成,并论述了它们的产地特征. 相似文献