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1.
Many sapphire and ruby occurrences are spatially linked with orogenic belts such as the Pan-African Orogen, the Himalayas, and regions of active or former subduction along the western margin of the Pacific Ocean. These gemstones have oxygen isotope compositions (δ18O) that span >45‰, reflecting the wide range of environments and conditions involved in corundum (Al2O3) formation. We compiled a global data base of sapphire and ruby δ18O, from which the following major groups of gemstones emerge: a dominant population of sapphires with δ18O centred around 5.5‰ (the mantle value) that is spatially related to regions of former subduction; a lesser population of sapphires and rubies with slightly higher δ18O that are associated with skarn and pegmatite; rubies with relatively low δ18O of 0‰–7‰ that occur in hydrothermally altered ultramafic metamorphic rocks in collision zones; and rubies with high δ18O of 14‰–25‰ that are found, almost exclusively, in Himalayan marble. The spatial distribution of the δ18O groups relative to plate boundaries provides insight into the two major periods of continental collision involved in sapphire and ruby formation: the Ediacaran collision of East and West Gondwana (the East African Orogeny) and the Cenozoic collision of India and Asia.  相似文献   

2.
The oxygen isotopic composition of gem corundum was measured from 22 deposits and occurrences in Madagascar to provide a gemstone geological identification and characterization. Primary corundum deposits in Madagascar are hosted in magmatic (syenite and alkali basalt) and metamorphic rocks (gneiss, cordieritite, mafic and ultramafic rocks, marble, and calc-silicate rocks). In both domains the circulation of fluids, especially along shear zones for metamorphic deposits, provoked in situ transformation of the corundum host rocks with the formation of metasomatites such as phlogopite, sakenite, and corundumite. Secondary deposits (placers) are the most important economically and are contained in detrital basins and karsts. The oxygen isotopic ratios (18O/16O) of ruby and sapphire from primary deposits are a good indicator of their geological origin and reveal a wide range of δ18O (Vienna Standard Mean Ocean Water) between 1.3 and 15.6‰. Metamorphic rubies are defined by two groups of δ18O values in the range of 1.7 to 2.9‰ (cordieritite) and 3.8 to 6.1‰ (amphibolite). “Magmatic” rubies from pyroxenitic xenoliths contained in the alkali basalt of Soamiakatra have δ18O values ranging between 1.3 and 4.7‰. Sapphires are classified into two main groups with δ18O in the range of 4.7 to 9.0‰ (pyroxenite and feldspathic gneiss) and 10.7 to 15.6‰ (skarn in marble from Andranondambo). The δ18O values for gem corundum from secondary deposits have a wide spread between −0.3 and 16.5‰. The ruby and sapphire found in placers linked to alkali basalt environments in the northern and central regions of Madagascar have consistent δ18O values between 3.5 and 6.9‰. Ruby from the placers of Vatomandry and Andilamena has δ18O values of 5.9‰, and between 0.5 and 4.0‰, respectively. The placers of the Ilakaka area are characterized by a huge variety of colored sapphires and rubies, with δ18O values between −0.3 and 16.5‰, and their origin is debated. A comparison with oxygen isotope data obtained on gem corundum from Eastern Africa, India, and Sri Lanka is presented. Giant placer deposits from Sri Lanka, Madagascar, and Tanzania have a large variety of colored sapphires and rubies with a large variation in δ18O due to mingling of corundum of different origin: mafic and ultramafic rocks for ruby, desilicated pegmatites for blue sapphire, syenite for yellow, green, and blue sapphire, and skarn in marbles for blue sapphire.  相似文献   

3.
Summary ?Mong Hsu rubies of the “trapiche” type are sporadically seen in the gem market. However, they have never been described in the field. The study of the nature of solid inclusions, the variation of trace-element contents, as well as the cathodoluminescence behaviour of six “trapiche” rubies permit the conclusion that these rubies crystallised in the same geological environment (marble-type deposit) as the normal rubies from Mong Hsu: (1) Cr and V are the main chromophorous elements in both ruby types; they act, together with Ti, as activators or quenchers for cathodoluminescence; (2) calcite, dolomite, rutile, mica, diaspore, apatite, chlorite, and feldspar are solid inclusions found in both ruby types; (3) the presence of bastn?site in trapiche ruby and fluorite in non-trapiche ruby indicates the circulation of F-bearing fluids during ruby deposition; (4) the distribution of trace-element contents in the crystal is similar for both ruby types. In the Cr2O3 vs. Fe2O3 and Cr2O3 vs. Fe2O3/TiO2 diagrams, the population fields of Mong Hsu “trapiche” and non-“trapiche” rubies overlap. They are distinct from those of rubies and sapphires hosted in basalts from South-east Asia. Received October 30, 2001; revised version accepted March 25, 2002  相似文献   

4.
Madagascar is one of the most important gem-producing countries in the world, including ruby and sapphires. Gem corundum deposits formed at different stages in the geological evolution of the island and in contrasting environments. Four main settings are identified: (1) Gem corundum formed in the Precambrian basement within the Neoproterozoic terranes of southern Madagascar, and in the volcano-sedimentary series of Beforona, north of Antananarivo. In the south, high-temperature (700 to 800 °C) and low-pressure (4 to 5 kbar) granulites contain deposits formed during the Pan-African orogenesis between 565 and 490 Ma. They accompany mafic and ultramafic complexes (ruby deposits of the Vohibory group), skarns at the contact between Anosyan granites and the Proterozoic Tranomaro group (sapphire deposits of the Tranomaro–Andranondambo district), and shear-zone corridors cross-cutting feldspathic gneisses, cordieritites and clinopyroxenites in the Tranomaro, Vohimena and Androyan metamorphic series (biotite schist deposits of Sahambano and Zazafotsy, cordieritites of Iankaroka and Ambatomena). The circulation of fluids, especially along discontinuities, allowed in-situ alkaline metasomatism, forming corundum host rocks related to desilicified granites, biotitites, “sakenites” and “corundumites”. (2) Gem corundum also occurs in the Triassic detrital formations of the Isalo group, as giant palaeoplacers in the Ilakaka–Sakaraha area. Here, sapphires and rubies may come from the metamorphic granulitic terranes of southern Madagascar. (3) Gem corundum deposits occur within the Neogene-Quaternary alkali basalts from Ankaratra (Antsirabe–Antanifotsy area) and in the Ambohitra Province (Nosy Be, Ambato and Ambondromifehy districts). Primary deposits are rare, except at Soamiakatra where ruby in gabbroic and clinopyroxenite xenoliths within alkali-basalts probably derive from mantle garnet peridotites. The blue-green-yellow sapphires typical of basaltic fields are always recovered in palaeoplacer (in karst formed upon Jurassic limestones from the Montagne d'Ambre, Antsiranana Province) and alluvial and soil placers (Ankaratra volcanic massif). (4) Deposits occur within Quaternary eluvial, colluvial and alluvial concentrations, such as high-quality rubies from the Andilamena and Vatomandry deposits.  相似文献   

5.
Oxygen isotope signatures of ruby and sapphire megacrysts, combined with trace-element analysis, from the Mbuji-Mayi kimberlite, Democratic Republic of Congo, and the Changle alkali basalt, China, provide clues to specify their origin in the deep Earth. At Mbuji-Mayi, pink sapphires have δ18O values in the range 4.3 to 5.4‰ (N = 10) with a mean of 4.9 ± 0.4‰, and rubies from 5.5 to 5.6‰ (N = 3). The Ga/Mg ratio of pink sapphires is between 1.9 and 3.9, and in rubies, between 0.6 and 2.6. The blue or yellow sapphires from Changle have δ18O values from 4.6 to 5.2 ‰, with a mean of 4.9 ± 0.2‰ (N = 9). The Ga/Mg ratio is between 5.7 and 11.3. The homogenous isotopic composition of ruby suggests a derivation from upper mantle xenoliths (garnet lherzolite, pyroxenite) or metagabbros and/or lower crustal garnet clinopyroxenite eclogite-type xenoliths included in kimberlites. Data from the pink sapphires from Mbuji-Mayi suggest a mantle origin, but different probable protoliths: either subducted oceanic protolith transformed into eclogite with δ18O values buffered to the mantle value, or clinopyroxenite protoliths in peridotite. The Changle sapphires have a mantle O-isotope signature. They probably formed in syenitic magmas produced by low degree partial melting of a spinel lherzolite source. The kimberlite and the alkali basalt acted as gem conveyors from the upper mantle up to the surface.  相似文献   

6.
Subordinate sapphire accompanies prevalent zircon megacrysts in the Bo Loei basaltic gem field, Ratanakiri Province, Cambodia. These deposits are important for heat-treated gem zircon. Dark blue sapphire, with rare blue-green, orange-brown and yellow stones, up to a few cm in size, include hexagonal-shaped and growth-zoned crystals. Analyses of the sapphires (electron microprobe and laser ablation-inductively coupled plasma-mass spectrometry) showed Fe as the main chromophore (0.6–2.7 wt%), with minor Ti (<0.7 wt%). Sapphire cores show enrichment in Fe relative to rims and some include exotic heavy elements (Nb up to 56, Ta up to 144, Sn up to 5 ppm). The sapphires show high Ga values (271–724 ppm) and Ga/Mg ratios (4.8–77.0) suggesting magmatic associations. Two sapphires with syngenetic inclusions (zircon, Nb-rich rutile) gave U–Pb (Th-disequilibrium corrected) ages at ca 0.93 ± 0.1 Ma. The Bo Loei sapphires show higher Fe and Ga than other magmatic sapphire suites elsewhere in Cambodia (Pailin), Laos (Ban Huai Sai, Ban Sam Sai), South Vietnam (Dak Nong, Dak Lac) and SE Thailand (Chanthaburi-Trat). This suggests potential for geographic typing of sapphire suites between these different fields.  相似文献   

7.
天然红宝石和蓝宝石的包裹体中常见典型的含水矿物包裹体,这些含水矿物包裹体容易受外界环境升温而发生改变。微量含水矿物包裹体变化会对红宝石和蓝宝石的物理和化学性质产生明显影响,该性质为宝石热处理的鉴定提供了检测思路。本文采集了天然红宝石和蓝宝石样品,用显微镜放大观察包裹体特征,结合红外光谱与显微共焦激光拉曼光谱测试研究了含水矿物包裹体的特征。结果表明:天然红宝石和蓝宝石样品中含水矿物包裹体的外观轮廓清晰,晶形完整;红外光谱在2000～3700cm~(-1)附近显示出2105～2110cm~(-1)和1977～1985cm~(-1)硬水铝石和3619cm~(-1)和3696cm~(-1)高岭石等水(H_2O或—OH等)的特征吸收峰;拉曼光谱中可见角闪石、云母、磷灰石和长石等结晶度较好的典型含水矿物包裹体的特征拉曼位移。该系列特征揭示了红宝石和蓝宝石样品中含有水的特征,可作为红宝石和蓝宝石天然成因且未经过热处理的鉴定依据。  相似文献   

8.
Orissa is an important area for gem variety of corundum deposits in India. Spectroscopic studies, such as ESR, OAS on samples from Sardapur, Orissa, were carried out to ascertain the colour cause of corundum. Electron spin resonance (ESR) spectroscopic study was carried out on the samples to detect the presence of paramagnetic ions i.e. Fe2+, Fe3+, Ti4+, Cr3+ and V3+ etc. The variable temperature experiment carried out to observe the effect of heating on peak valence state change in paramagnetic ions. Samples were cut and polished to obtain the optical absorption spectrum (OAS) to detect the colour causing transition ions/defect centres. The samples of gem variety were step heated up to 300°C for colour enhancement studies. EPMA analysis has revealed the low chromium concentration in the rubies. The varying hues of red in the corundum are due to the presence of bivalent and trivalent iron and charge transfer process along with Cr3+ absorption in the 550 nm region.  相似文献   

9.
元江红宝石的呈色机理和改色效果   总被引：1，自引：0，他引：1  
钱云葵 《云南地质》2004,23(3):337-342
元江红宝石属区域变质成因大理岩型，与著名的缅甸抹谷红宝石矿床的成因类型几乎完全一致。该矿红宝石的颜色中，浅红、浅玫瑰红、及无色刚玉占总量的50％，提高该矿的潜在经济价值，增加红宝石的色调饱合度和消除色调不正的现象，必须研究红宝石呈色机理。电子探针分析结果为改色工艺提供依据。通过实验表明，浅玫瑰红的红宝石改色效果明显。  相似文献   

10.
The G ksun Ophiolites in Do an ehir area (Malatya-Southern Turkey) contain corundum mineralizations with significant gem-quality (ruby). Modal mineralogical composition of ruby-bearing rocks consists of hornblende (65%-70 %), plagioclase (20%-25%), green garnet (4%-5 %), ruby (2%-3%), and opaque minerals (<1%). Although ruby shows varying colors in the groundmass, it is generally colorless and rarely very pale pink and has high relief. It has no cleavage but rotund fractures. It has highest interference colors and twinning in some poly-prismatic crystals under the microscope. Crystal sizes range from 2x10 mm up to 30x50 mm. The most remarkable properties are red to pink in color, low to medium transparency, medium to big crystal sizes, lamellar and deformation twinning, secondary liquid feathers, hollow tubes, mineral inclusions, asterism, high birefringence and refractive indices and specific gravity. Rubies show crimson red cathodoluminescence colors activated by Cr3+ in the crystal structure, which is confirmed by the Electron Probe Microanalyses (EPMA). Tectonic setting, geological environment, petrographical, mineralogical, geochemical and gemological characteristics of rubies suggest that the Do an ehir ruby mineralization can be classified into the amphibolite-hosted type of corundum deposits of Tanzania.  相似文献   

11.
针对目前市场上出现的一些因优化处理而产生轻微玻璃残余物的天然红宝石,经适当浓度的氢氟酸(浓度23%)浸泡后,位于红宝石内裂隙和表面凹坑中的轻微玻璃态残余物被溶解,达到清理玻璃态残余物的目的,并利用电感耦合等离子体-原子发射光谱仪(ICP-AES)分析含玻璃材料的溶液中Si和Al的浓度分别为28.60μg/mL和2.795μg/mL,进而估算玻璃态残留物的损失量以判定热处理过程中非人为加入的玻璃态物质在红宝石中的充填程度。利用红外光谱仪对玻璃残留物清理前后的红宝石红外光谱进行对比研究得出:清理前,红外光谱显示在1 100~1 000 cm-1内有1个单峰宽谱带,谱峰为1 050 cm-1,是由νas(Si—O—Si)非对称伸缩振动引起的,表明残留物为非晶质体,750~600 cm-1之间位于744 cm-1的吸收峰为νs(Si—O—Si)对称伸缩振动引起;清理后,未检测到玻璃残余物特征的Si—O振动峰,仅具950~600 cm-1范围内的宽谱带,为刚玉Al—O基频振动谱带736、622 cm-1,体现晶质金属氧化物的特征,表明样品中玻璃态物质已被清除,实验后红宝石可被划归为经人工优化范畴。宝石显微镜下观察到清理实验后红宝石中原先被玻璃残余物所掩盖的显著内裂隙及表面凹坑。  相似文献   

12.
Mineral inclusions of corundum are reported from diamonds from alluvial deposits of tributaries of the Rio Aripuanã, Juina, Brazil. We present the first recorded occurrence of sapphire as an inclusion in diamond and expand on the database of ruby and white corundum inclusions. Ruby inclusions are found to occur both as isolated and touching grains with aluminous pyroxene and associated with ferropericlase. Mineral chemistry and phase relations place the origin of such ruby-bearing diamonds within the lower mantle at 770 km. Mineral associations indaving other corundum inclusions were not observed; hence, their depth of origin is less certain.

Compositions of corundum samples were characterised by electron and ion microprobe. Given the scarcity of literature data, corundum samples from a variety of other geological settings were also analysed. Samples comprised corundums associated with granitic emplacement, metasomatism, amphibolite-facies and granulite-facies rocks, gem and industrial synthetic origins and carmine-coloured corundums recovered from kimberlite drill cores.

In addition to variable amounts of Cr, Fe, Ti, Mg and Si, measurable quantities of other transition elements and high field strength elements were also detected. Corundums from similar geological settings show very similar compositions and are easily distinguishable from other settings. Irrespective of locality, rubies from Norwegian, Tanzanian and Kenyan amphibolite-facies rocks are compositionally indistinguishable. Additionally, corundums from metasomatised zones associated with contact metamorphism from Arizona and Japan were very similar, particularly characterised by unusually high abundance of mobile Zr and Nb (tens of ppm). All Juina inclusions are particularly distinguishable from other corundums by high concentrations of Ni (18–171 ppm weight), typically at least an order of magnitude enriched over the same corundum varietal types from elsewhere. Furthermore, the sapphire inclusion exhibited much larger ratios of Ga and Ge to HFSE elements compared to otherwise similar samples, and ruby inclusions are distinguished by high Mg/Fe ratios (0.27–1.56 by weight). Compositional differences between inclusions in diamonds and corundums from other settings in addition to corundum's physical and chemical durability suggest that with the employment of rapid identification tools such as energy dispersive spectrometry (EDS) and laser-ICPMS, corundum has promise as an indicator of diamond prospectivity.  相似文献   


13.
龙楚 《岩石矿物学杂志》2014,33(S2):147-154
通过显微镜下观察充填红宝石内外部的充填特征、次生玻璃的形态,结合在Diamond ViewTM荧光成像仪下观察红宝石基底及次生玻璃体的发光情况,对红宝石中玻璃质材料充填的"量"进行了判断.将红宝石的充填程度分为轻微充填、中度充填、明显充填3等,建议对应定名为红宝石(备注可见轻微充填现象)、红宝石(备注可见中度充填现象)、充填处理红宝石.  相似文献   

14.
An attempt has been made to interpret natural sapphire optical absorption spectra with regard to the exchange-coupled pairs of iron impurities in their ferric and ferrous states. Level schemes have been calculated for Fe3+-Fe3+ and Fe2+-Fe2+ pairs of all the orders, their symmetry being observed. The selection rules are discussed. EPR and infrared spectroscopy information has been used to assist the optical spectroscopy data. The sapphire color has been interpreted as a function of Fe2+/Fe3+ ratios and of the presence of their pairs in the stone. The various types of charge compensation in Fe2+→Al3+ isomorphism are discussed.  相似文献   

15.
Megacrystic sapphires are frequently associated with alkaline basalts, most notably in Asia and Australia, although basalt is not generally normative in corundum. Most of these sapphire occurrences are located in alluvial or eluvial deposits, making it difficult to study the enigmatic relationship between the sapphires and their host rocks. Here, we present detailed petrological and geochemical investigations of in situ megacrystic sapphires within alkaline basalts from the Cenozoic Siebengebirge Volcanic Field (SVF) in Germany. Markedly, the sapphires show several micrometer thick spinel coronas at the contact with the host basalt, indicating chemical disequilibrium between the sapphire and the basaltic melt, supporting a xenogenetic relationship. However, in situ U–Pb dating of a Columbite Group inclusion within one Siebengebirge sapphire using laser ablation–inductively coupled plasma–mass spectrometry (LA–ICP–MS) indicates a close genetic relationship between sapphire crystallization and alkaline mafic volcanism in the SVF. The syngenetic mineral inclusion suite including carbonates, members of the Pyrochlore, Betafite and Columbite Groupe minerals, as well as a high abundance of HFSE and of gaseous low-density CO2 inclusions support a parentage of a highly evolved, MgO and FeO deficient carbonatitic melt. We identified CO2 to be the link between alkaline basaltic volcanism and the xenocrystic sapphires. Only alkaline volcanic suites can build up enough CO2 in this magma chamber upon fractionation so that at high degrees of fractionation a carbonatitic melt exsolves which in turn can crystallize sapphires.  相似文献   

16.
颜色是软玉价值的重要体现,青海软玉颜色丰富,而致色方面的研究较为滞后。近年来青海软玉致色研究多为翠青玉和烟青玉,认为Cr~(3+)和Mn~(2+)分别为翠青玉和烟青玉致色元素。青海软玉的颜色非单一色彩,如青白色、翠绿色、灰紫色等,因此青海软玉致色应包含多种致色元素。本文在前人研究的基础上,利用X射线荧光光谱法(XRF)、化学滴定法、电感耦合等离子体质谱法(ICP-MS)和电子顺磁共振能谱(EPR)测试数据,根据分析数据与色调变化之间的关系揭示了8种颜色青海软玉的致色元素。结果表明:白玉致色元素为Fe~(3+);青白玉和碧玉致色元素为Fe~(2+)和Fe~(3+);青玉致色元素为Fe~(2+)、Fe~(3+)和高价态的Mn;翠青玉致色元素为Fe~(2+)、Fe~(3+)、Cr~(3+);黄玉和糖玉致色元素为Fe~(3+)和高价态的Mn;烟青玉致色元素为Fe~(3+)和Ti~(4+)。研究认为青海软玉中绿色调与Fe~(2+)有关,黄色调与Fe~(3+)和高价态的Mn有关,而蓝紫色调与Fe~(3+)和Ti~(4+)有关。本研究基本确定了不同颜色青海软玉的致色元素,为青海软玉致色机制的研究提供了理论依据。  相似文献   

17.
Studies of serial suites of samples collected along six sections measured across the width of an amphibolite body, some 750 meters thick, reveal (1) the presence of a hornblende concentration near the presumed base of the body, (2) an upward sodium-enrichment trend reflected by plagioclase, and (3) an upward iron-enrichment trend reflected by variation in 100Mg/Mg+Fe2+Fe3+Mn values for hornblende. Consistent with field evidence, the data indicate formation of the amphibolite by metamorphism of a tabular mafic igneous body. The mineralogic variations are suggestive of those expected during the differentiation of a mafic sill in which the trends are controlled by early crystallization and subsequent gravitational accumulation of pyroxene. In addition to indicating igneous parentage, these variations establish the stratigraphic sequence.  相似文献   

18.
Gem corundum, a minor but persistent megacryst in east Australian basalt fields, is mined from some placer concentrations. Laser ablation, inductively coupled plasma mass spectrometry analyses and O isotope determinations on a colour range of corundum from different fields, show that chromophore (Fe, Cr, Ti, V) and genetic indicator (Ga, Mg, δ18O) values can distinguish corundum sources (magmatic, metamorphic and metasomatic) before basalt incorporation. They also characterise corundum groups from different fields. This identified two metamorphic groups, one carrying ruby at Barrington Tops, and a magmatic group distinct from those from other gem fields (lower Fe, northeast Tasmania; higher Fe, Yarrowitch). Ruby-bearing groups show clear provincial characteristics and include lower temperature spinel-facies groups (Barrington, Yarrowitch) and higher temperature garnet-facies groups (Cudgegong–Macquarie River). High Mg/Fe and Ni values in the latter approach those for corundum in diamond, and are a possible diamond indicator. The corundum derived from diverse fold-belt and felsic sources in underlying lithosphere forms a dataset for comparing corundum from other basalt fields.  相似文献   

19.
A calcite-marble containing gem-quality ruby is exposed in the Hunza Valley, northwestern part of the Karakoram mountains, Pakistan zone of Kashmir. The marble forms concordant intercalations within sillimanite- and garnet-bearing biotite-plagioclase gneisses and mica schists. The metamorphic sequence is cut by discordant aplite and pegmatite dikes. The following mineral assemblages are recognized in the marble:1) Calcite+corundum+phlogopite±margarite±sheridanite±Al-rich pargasite±anorthite (An 96.7),2) calcite+spinel±corundum+phlogopite+sheridanite.Microprobe analyses are given for the essential minerals including corundum (ruby) and three different colour varieties of spinel. On the basis of recent experimental data, especially in the system CaO - Al2O3 - SiO2 - H2O -CO2 (and related subsystems), we assume that, during the regional metamorphism, temperatures of about 600 – 620°C and a water vapour pressure of about 6 kb were realized in part of the Hunza area. The gas phase must have contained roughly 20 mole-% of CO2. Thus the total fluid pressure may have reached about 7 kb. Presumably, temperatures increased in northwest direction, perhaps up to about 700°C. The estimated P-T conditions are consistent with a geothermal gradient of about 25°C/km.  相似文献   

20.
The subsolidus phase relationships of magnetite, hercynite,hematite, corundum, wostite, and iron are described. The phaseswere synthesized from chemical mixtures. Reactions and solidsolution between them were induced under controlled conditionsof composition, temperature, total vapor pressure, and partialpressure of oxygen. Reaction rates are slow, so that the experimentslasted from 1 to 40 days, and quenching is completely successful. A solvus was determined which limits solid solution along themagnetitc-hercynite join at temperatures below 860o?15oC. Compositionsof the spinel solid solutions were determined by measuring theshift of the (440) reflection, using a powder X-ray diffractometer.The calibration curve, 20 vs. composition, was made from measurementsof spinel solid solutions synthesized in the one-phase region.The cell edge ao changes from 8–391?0.002 A (magnetic,Fe+2Fe2+2O4OJ to 8.150?0.004 (hercynite, Fe+2Al2O4)by ao?8.391–0.00190x- 0.5X210-5 (X is mol per cent FeAl2O4 in solid solution). In the system Fe-Al2-O3-O there are five univariant assemblages: 1. Hematite-corundum+magnetite +V (vapor) 2. Corundum+magnetite+hercynite+V 3. Magnetite+hercynite+w?stite+V 4. Hercynite+wilstite+iron+V 5. Hercynite+iron+corundum+V The lines were located by determining the composition of themagnetite, hercynite, hematite, and corundum solid solutionsfor each assemblage. The diagrams provide a basis for the discussion of the paragenesisof the oxide minerals. The progressive metamorphism of lateritedeposits can be represented by (1) laterites and bauxites: hematiteH+hydratedaluminum oxides; (2) diasporites: hematite+diaspore+corundum,with magnetite as a rare accessory; (3) emery: corundum+magnetite,with hematite as an accessory. The path of these mineral changeson the diagrams shows the decrease in oxygen content of thesolids with decrease in the partial pressure of oxygen and relatesthe aluminum content of the magnetite to temperature. The occurrences of hercynite are discussed. It is a rare mineralbecause it requires unusual conditions to grow, i.e. relativelylow oxygen pressure and an extremely Fe-Al-rich environment.  相似文献   

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