Dielectric constants of tephroite,fayalite and olivine and the oxide additivity rule

The dielectric constants and dissipation factors of synthetic tephroite (Mn₂SiO₄), fayalite (Fe₃SiO₄) and a forsteritic olivine (Mg_1.80Fe_0.22SiO₄) were measured at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: tephroite, κ′_a= 8.79 tan δ_a = 0.0006 κ′_b = 10.20 tan δ_b = 0.0006 κ′_c= 8.94 tan δ_c= 0.0008 fayalite, gk′_a = 8.80 tan δ_a = 0.0004 gk′_b= 8.92 tan δ_b = 0.0018 gk′_c = 8.58 tan δ_c = 0.0010 olivine, gk′_a = 7.16 tan δ_a = 0.0006 gk′_b = 7.61 tan δ_b = 0.0008 gk′_c = 7.03 tan δ_c = 0.0006 The low dielectric constant and loss of the fayalite indicate an exceptionally low Fe³⁺ content. An FeO polarizability of 4.18 ų, determined from α_D(FeO) = [α_D (Fe₂SiO₄)-α_D(SiO₂)]/2, is probably a more reliable value for stoichiometric FeO than could be obtained from Fe_xO where x = 0.90–0.95. The agreement between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of oxide polarizabilities according to α_D(M₂M′X₂) = 2α_D(MX) + α_D(M′X₂) is ～+2.8% for tephroite and +0.2% for olivine. The deviation from additivity in tephroite is discussed.     

Dielectric constants of topaz,orthoclase and scapolite and the oxide additivity rule

The dielectric constants and dissipation factors of topaz, scapolite and orthoclase were determined at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: topaz κ′ _a =6.61 tan δ=0.0005 κ′ _b =6.82 tan δ=0.0007 κ′ _c =6.81 tan δ=0.0007 orthoclase κ′ _a =4.69 tan δ=0.0007 κ′ _b =5.79 tan δ=0.0007 κ′ _c =5.63 tan δ=0.0011 κ′ ₁₁ =4.72 κ′ ₂₂ =5.79 κ′ ₃₃ =5.76 scapolite κ′ _a =6.74 tan δ=0.0004 κ′ _c =8.51 tan δ=0.0004 The deviation (Δ) between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of ion polarizabilities according to α _D (mineral)=∑α_D (ions) for topaz is 2.5%. The large deviations of orthoclase and scapolite from the oxide additivity rule with δ=+7.2 and + 17.6%, respectively, are attributed to “rattling” K ions in orthoclase and “rattling” (Na,K,Ca) ions and disordered O⁼ and Cl^- ions in scapolite.     

Dielectric constants of chrysoberyl,spinel, phenacite,and forsterite and the oxide additivity rule

The dielectric constants and dielectric loss values of BeAl₂O₄ (chrysoberyl), MgAl₂O₄ (spinel), Be₂SiO₄ (phenacite), and Mg₂SiO₄ (forsterite) were measured at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: chrysoberyl, κ′ _a =9.436, κ′ _b =9.071, κ′ _c =8.269; spinel, κ′ _a =8.18; phenacite, κ′ _a =6.28, κ′ _c =6.06; and forsterite, κ′ _a =6.867, κ′ _b =7.392, κ′ _c =6.739. The agreement between measured dielectric polarizabilities as determined from the Clausius-Mosotti equation and those calculated from the sum of oxide polarizabilities according to α_D(M₂M′X₄) = 2α_D(MX)+α_D(M′X₂) is ~ 1.0%.     

Dielectric constants of crystalline and amorphous spodumene,anorthite and diopside and the oxide additivity rule

The dielectric constants and dissipation factors of LiAlSi₂O₆, CaAl₂Si₂O₈ and CaMgSi₂O₆ in both the crystalline (α-spodumene, anorthite, and diopside) and amorphous forms were determined at 1 MHz using a two-terminal method and empirically determined edge corrections. The results are: spodumene κ′ ₁₁=7.30 tan δ= 0.0007 κ′₂₂=8.463 tan δ= 0.0002 κ′₃₃ =11.12 tan δ= 0.0007 anorthite κ′ _a ^*=5.47 tan δ= 0.0009 κ′_b ^*=8.76 tan δ= 0.0010 κ′_c ^*=7.19 tan δ= 0.0013 diopside κ′₁₁=9.69 tan δ= 0.0016 κ′₂₂ = 7.31 tan δ= 0.0007 κ′₃₃=7.29 tan δ= 0.00019 LiAlSi₂O₆ κ′=8.07 tan δ= 0.047 amorphous CaAl₂Si₂O₈ κ′=7.50 tan δ= 0.0024 amorphous CaMgSi₂O₆ κ′=8.89 tan δ= 0.0021 amorphous The dielectric properties of a spodumene glass, progressively crystallized at different conditions, were also determined. As the crystallization temperature was increased from 720 to 920° C, κ′ increased from 6.22 to 6.44. The dissipation factor, tan δ, remained constant at 0.020. Similarly, as the crystallization time at 750° C increased from 0.5 hr to 6.0 hr, κ′ increased from 6.28 to 6.35. The deviations of the measured dielectric polarizabilities as determined from the Clausius-Mosotti equation from those calculated from the sum of oxide polarizabilities according to α _D(mineral, glass) = σ α _D(oxides) are +7.4% for α-spodumene, +1.2% for diopside, and +28.0, +19.6 and +15.9% for amorphous spodumene, anorthitie and diopside compositions, respectively. Positive deviations in α-spodumene and anorthite are consistent with lower than normal apparent cation bond valence sums and are believed to be evidence for loosely bonded “rattling” Li and Ca ions. Diopside, with Ca and Mg ions having normal bond valence sums, exhibits no abnormal deviation from additivity. Larger positive deviations in amorphous SiO₂, LiAlSi₂O₆, CaAl₂Si₂O₈ and CaMgSi₂O₆ are postulated to arise from a combination of loosely bonded cations and disordered O⁼ ions where the oxygen dielectric polarizability increased from its normal value of 2.0 ų in well-behaved oxides to 2.2–3.0 Å₃ in the amorphous phases.     

Dielectric constants of BeO,MgO, and CaO using the two-terminal method

Using fused SiO₂, CaF₂, and SrF₂ samples with accurately known dielectric constants, we have evaluated the accuracy and precision of two-terminal dielectric constant measurements on small single crystals using empirically determined edge corrections. Values of κ′ at 1 MHz of 3.836±0.05 for silica, 6.814±0.07 for CaF₂ and 6.463±0.09 for SrF₂ indicate an accuracy and precision of 1.0–1.5% for samples having areas of 0.05–1.0 cm². Dielectric constants of BeO, MgO, and CaO measured by this technique are: BeO, κ′_a=6.87 and κ′_c=7.74; MgO, κ′= 9.90; and CaO, κ′=11.95 where κ′_a and κ′_c are the dielectric constants parallel to the a and c axes, respectively. Dielectric loss measurements on CaO in vacuum between 5–400 K at 10–10⁵ Hz indicate significant dispersion at temperatures higher than 300 K, but the effect of the losses on the dielectric constant is less than 1% at 1 MHz and 300 K.     

东海超高压榴辉岩中绿帘石、褐帘石、磷灰石和钍石集合体的电子探针成分和化学定年研究

中国大陆超深钻(CCSD)主孔从100米到3000米切穿含柯石英榴辉岩,为系统研究大陆深俯冲过程中含稀土元素副矿物提供了机会。本文报道了该钻孔榴辉岩存在发现的绿帘石、褐帘石、磷灰石和钍石复合颗粒。它们以同心环带结构为特征,从边部向中心依次为绿帘石、褐帘石和磷灰石;钍石既可包裹再磷灰石中,也可见于褐帘石中。电子探针分析显示,褐帘石不仅含有较高的轻稀土元素(LREE2O3=23．36wt％),而且可含有2．6wt％ThO2。根据绿帘石和褐帘石的电子探针高分辨U、Th、Pb成分计算得到绿帘石边部的形成年龄为738±88Ma,该年龄与大别-苏鲁地体榴辉岩的元古代源岩的年龄相当,因此,绿帘石可能为残留相。相反,褐帘石的年龄为220±41Ma,与大别-苏鲁超高压变质年龄相近。因此,褐帘石与磷灰石和钍石一起应该为超高压变质事件的产物。根据绿帘石、褐帘石及其共生的磷灰石和钍石的结构、成分特征和化学定年结果,我们推测绿帘石与可能已完全消耗的独居石很可能为变质副矿物组合的先驱矿物。独居石-绿帘石复合颗粒在榴辉岩相高压／超高压变质过程中反应形成磷灰石+钍石+褐帘石组合。     

Petrogenesis of lawsonite and epidote eclogite and blueschist, Sivrihisar Massif, Turkey

The Sivrihisar Massif, Turkey, is comprised of blueschist and eclogite facies metasedimentary and metabasaltic rocks. Abundant metre‐ to centimetre‐scale eclogite pods occur in blueschist facies metabasalt, marble and quartz‐rich rocks. Sivrihisar eclogite contains omphacite + garnet + phengite + rutile ± glaucophane ± quartz + lawsonite and/or epidote. Blueschists contain sodic amphibole + garnet + phengite + lawsonite and/or epidote ± omphacite ± quartz. Sivrihisar eclogite and blueschist have similar bulk composition, equivalent to NMORB, but record different P–T conditions: ～26 kbar, 500 °C (lawsonite eclogite); 18 kbar, 600 °C (epidote eclogite); 12 kbar, 380 °C (lawsonite blueschist); and 15–16 kbar, 480–500 °C (lawsonite‐epidote blueschist). Pressures for the Sivrihisar lawsonite eclogite are among the highest reported for this rock type, which is rarely exposed at the Earth's surface. The distribution and textures of lawsonite ± epidote define P–T conditions and paths. For example, in some lawsonite‐bearing rocks, epidote inclusions in garnet and partial replacement of matrix epidote by lawsonite suggest an anticlockwise P–T path. Other rocks contain no epidote as inclusions or as a matrix phase, and were metamorphosed entirely within the lawsonite stability field. Results of the P–T study and mapping of the distribution of blueschists and eclogites in the massif suggest that rocks recording different maximum P–T conditions were tectonically juxtaposed as kilometre‐scale slices and associated high‐P pods, although all shared the same exhumation path from ～9–11 kbar, 300–400 °C. Within the tectonic slices, alternating millimetre–centimetre‐scale layers of eclogite and blueschist formed together at the same P–T conditions but represent different extents of prograde reaction controlled by strain partitioning or local variations in fO₂ or other chemical factors.     

Coexisting zoisite and clinozoisite in biotite schists from the Hohe Tauern,Austria

Coexisting zoisite and clinozoisite assemblages in biotite schists from the western Hohe Tauern, Austria, have been investigated with the electron microprobe, polarization optics, and X-ray diffractometer. Zoisite and clinozoisite show slight compositional zoning, ranging from the core to the rim from about 1.8 to 1.0 wt. % Fe in zoisite, and 4.0 to 3.0 wt. % Fe in clinozoisite. The results suggest a gap of composition between coexisting zoisite and clinozoisite under greenschist-amphibolite transition facies conditions.The optical orientation and 2V of zoisite vary considerably within single grains. Lamellar structures have been detected which may be produced by unmixing of zoisite. The Fe-poor lamellae have 2V _z=20–50°, a dispersion r>v, and relatively low refringence, the Fe-rich lamellae have 2V _z =90–100°, rv, and higher refringence. The optic axial planes of both lamellae systems deviate from the (100) cleavage by up to 15°, and suggest a deviation from orthorombic symmetry. The lattice constants of coexisting zoisite and clinozoisite are given.     

热处理对黝帘石颜色的影响及其致色成因探讨——以坦桑尼亚黄色和蓝色黝帘石为例

坦桑尼亚的天然蓝紫色黝帘石(也被称为坦桑石)产量稀少,储量较低。然而,通过热处理优化改色后,黝帘石的经济价值会得到显著提升。但多年来,关于热处理后黝帘石的蓝紫色成因一直存在争议。本文选取天然的坦桑尼亚黄色及蓝色黝帘石为研究对象,通过设置300℃、400℃和500℃3个不同的温度条件,并利用L^*a^*b^*颜色参数对样品的颜色变化进行了量化分析。热处理前不同颜色黝帘石的宝石学特征具有一致性,热处理后结果表明,500℃左右的温度是浅蓝-蓝色黝帘石的最佳改色条件。经过热处理黝帘石的蓝紫色调明显增强,通过调整温度可有效调控样品中的黄色或褐色调。黄色黝帘石在热处理后展现出从黄褐色到蓝紫色的独特变色效应,而400~500℃是这一颜色变化的临界温度范围。结合EDXRF、LA-ICP-MS及UV-VIS等多种分析手段,认为天然黝帘石的蓝色主要由V³⁺和Ti³⁺导致,黄色则主要由Ti³⁺引起,V/Ti值在天然黝帘石的成因机制中起辅助作用。此外,热处理后黝帘石蓝紫色调的产生与增加以及黄色→蓝-蓝紫色的转变与Ti³⁺+V⁴⁺→Ti⁴⁺+V³⁺的电荷迁移密切相关。     

磁铁矿-磷灰石型铁矿的实验模拟研究进展与展望

磁铁矿-磷灰石(IOA)型铁矿,或称基鲁纳型(Kiruna)铁矿,或称陆相火山岩型铁矿,在时空上常常与碱性-钙碱性的(次)火山岩有着紧密联系。该类型矿床在世界范围内广泛产出,发育特征的磁铁矿-磷灰石-阳起石矿物组合,但其成因还存在广泛争议。文章介绍并归纳了成岩成矿实验在IOA型矿床相关的岩浆原生过程方面取得的最新进展,包括液态不混溶作用、岩浆磁铁矿-气泡悬浮模式和阳起石岩浆成因的实验验证,探讨了磁铁矿以及磷灰石通过液态不混溶作用和气泡悬浮完成超常富集形成铁矿浆的可能性。在此基础上,指出了相关实验目前尚存在的问题及未来的研究方向。     

Monazite, iron oxide and barite exsolutions in apatite aggregates from CCSD drillhole eclogites and their geological implications

We have identified abundant exsolutions in apatite aggregates from eclogitic drillhole samples of the Chinese Continental Scientific Drilling (CCSD) project. Electron microscope and laser Raman spectroscopy analyses show that the apatite is fluorapatite, whereas exsolutions that can be classified into four types: (A) platy to rhombic monazite exsolutions; (B) needle-like hematite exsolutions; (C) irregular magnetite and hematite intergrowths; and (D) needle-like strontian barite exsolutions. The widths and lengths of type A monazite exsolutions range from about 6-10 μm (mostly 6 μm) and about 50-75 μm, respectively. Type B exsolutions are parallel with the C axis of apatite, with widths ranging from 0.5 to 2 μm, with most around 1.5 μm, and lengths that vary dramatically from 6 to 50 μm. Type C exsolutions are also parallel with the C axis of apatite, with lengths of ∼30-150 μm and widths of ∼10 to 50 μm. Type D strontian barite exsolutions coexist mostly with type B hematite exsolutions, with widths of about 9 μm and lengths of about 60-70 μm. Exsolutions of types B, C and D have never been reported in apatites before. Most of the exsolutions are parallel with the C axis of apatite, implying that they were probably exsolved at roughly the same time. Dating by the chemical Th-U-total Pb isochron method (CHIME) yields an U-Pb isochron age of 202 ± 28 Ma for monazite exsolutions, suggesting that these exsolutions were formed during recrystallization and retrograde metamorphism of the exhumed ultrahigh pressure (UHP) rocks. Quartz veins hosting apatite aggregates were probably formed slightly earlier than 202 Ma. Abundant hematite exsolutions, as well as coexistence of magnetite/hematite and barite/hematite in the apatite, suggest that the oxygen fugacity of apatite aggregates is well above the sulfide-sulfur oxide buffer (SSO). Given that quartz veins host these apatite aggregates, they were probably deposited from SiO₂-rich hydrous fluids formed during retrogression of the subducted slab. Such SiO₂-rich hydrous fluids may act as an oxidizing agent, a feasible explanation for the high oxygen fugacity in convergent margin systems.     

An EXAFS study of Gd,Er and Lu site location in the epidote structure

L _III edge extended X-ray absorption fine structure (EXAFS) spectra of Gd, Er and Lu environments in synthetic epidotes of composition CaLa_0.9 X _0.1Al₂MgSi₃O₁₃H (X=Gd or Er or Lu) were recorded using synchrotron radiation. The Fourier transforms of the Gd-, Er- and Lu-EXAFS are clearly different from one another indicating wholly or partially different site occupancy. Model fitting of the Fourier-filtered partial EXAFS and comparison of pair distribution functions with those calculated for natural epidote leads to the conclusion that three different sites are probably involved in the accommodation of these elements in the epidote structure, and that site preference is a function of the rare earth ionic size. Gd is located in A2-type sites, whereas the local atomic environment of Er is consistent with A1 site occupancy and the Lu environment has been modelled on an M3-type octahedral site.     

Transformation of garnet epidote amphibolite to eclogite, western Dabie Mountains, China

Omphacite and garnet coronas around amphibole occur in amphibolites in the Hong'an area, western Dabie Mountains, China. These amphibolites consist of an epidote–amphibolite facies assemblage of amphibole, garnet, albite, clinozoisite, paragonite, ilmenite and quartz, which is incompletely overprinted by an eclogite facies assemblage of garnet, omphacite and rutile. Coronas around amphibole can be divided into three types: an omphacite corona; a garnet–omphacite–rutile corona; and, a garnet–omphacite corona with less rutile. Chemographic analysis for local reaction domains in combination with petrographical observations show that reactions Amp + Ab + Pg = Omp +Czo + Qtz + H₂O, and Amp + Ab = Omp ± Czo + Qtz + H₂O may lead to the development of omphacite coronas. The garnet–omphacite–rutile corona was formed from the reaction Amp + Ab + Czo + Ilm ± Qtz = Omp + Grt + Rt + H₂O. In garnet–omphacite coronas, the garnet corona grew during an early stage of epidote amphibolite facies metamorphism, whereas omphacite probably formed by the reactions forming the omphacite corona during the eclogite facies stage. It is estimated that these reactions occurred at 0.8–1.4 GPa and 480–610 °C using the garnet–clinopyroxene thermometer and omphacite barometer in the presence of albite.     

The influence of pressure on the OH valence vibration of zoisite

The influence of pressure on the OH-stretching vibration of zoiste has been studied by single crystal high pressure infrared spectroscopy. A band related to the OH-stretching vibration displayed a linear shift from 3170 cm^?1 at 1 bar to 2795 cm^?1 at 116 kbar. The half-band width increased linearly with respect to pressure from 60 cm^?1 at 1 bar to 500 cm^?1 at 116 kbar. The strength of the absorption of this band is strongly frequency dependent. The high-energy shift of a band at around 2200 cm^?1 on pressure increase indicates that this band is not due to a second OH-stretching vibration as previously suggested by Langer and Lattard (1980).     

Transitional blueschist–epidote amphibolite facies metamorphism in the Frankenberg massif, Germany, and geotectonic implications

Bimodal metavolcanic rocks, granitic gneisses and metasediments are associated in the Frankenberg massif, Germany. These rocks are faulted against underlying very low-grade Palaeozoic sequences and adjacent metamorphic complexes of the Variscan basement. The granitic gneisses record an Rb–Sr whole-rock isochron age of 461±20  Ma that is taken as at least a minimum protolith age. The bimodal meta-igneous suites are interpreted to have formed during rifting of the Gondwana continental margin in the Cambro-Ordovician. The various metamorphic units have all experienced a common P–T  history. The peak-pressure stage is constrained to around 490–520  °C and 10–14  kbar (10–12  kbar being most realistic). The metamorphism proceeded along a clockwise P–T path towards conditions of around 580–610  °C and 7–8.5  kbar at the thermal peak followed by a final low-pressure overprint which spanned amphibolite facies to prehnite–actinolite facies temperatures. Owing to a secondary Rb–Sr whole-rock isochron age of 381±24  Ma, interpreted to date the retrograde stage, the whole metamorphic cycle in the Frankenberg massif is ascribed to the late Silurian–early Devonian high-pressure event widely recorded in the European Variscides. The antiformal complexes bordering the Frankenberg massif underwent a well-documented early Carboniferous metamorphism, suggesting that the Frankenberg massif constitutes a klippe which was overthrust towards the end of this second metamorphic cycle.     

Synthesis of Fe-pumpellyite and its stability relations with epidote

Hydrothermal synthesis of Fe-pum-pellyites was conducted using high pressure cold-seal apparatus and solid oxygen buffering techniques at temperatures between 250°C and 550°C and 2.0–9.1 kbar P_fluid. Fe-pumpellyites were synthesized from partially crystalline gel mixtures of compositions: 4CaO - 2.1Al₂O₃_1.5FeO - 0.3MgO - 6SiO₂ (II) and 3CaO - 1.5 Al₂O₃ - 2.7FeO - 0.3MgO - 6SiO₂ (III) in the presence of excess H₂O at P_fluid of 5–9.1 Kbar, temperatures between 275°C and 325°C, and f_O2 defined by the QFM and HM buffers; for both of these compositions (II and III), the condensed synthetic run products included minor 7Å chlorite ± garnet ± Fe-oxide. The cell dimensions and aggregate refractive index (a= 19.13(2)Å, b= 5.940(4)Å, c= 8.847(5)Å, ±= 97.37(6)±, and n= 1.702(2)) of the pum-pellyite synthesized from the bulk composition II mix are compatible with those of natural pumpellyites containing similar total Fe contents. Attempts at synthesizing Fe-pumpellyites from a Mg-free bulk composition were not successful; these results are consistent with the total absence of natural Mg-free pumpellyites. The higher temperature, higher oxygen fugacity assemblages of the equivalent bulk compositions (II and III) consist of epidote ± minor amounts of chlorite, garnet, quartz, hematite, and magnetite. The results of these synthesis experiments accord with the mineral parageneses observed in low-grade metabasites which imply that Fe-pumpellyites are replaced by epidote with increasing temperature and/or f_O2 and that Fe³⁺ is preferentially partitioned into epidote with respect to coexisting pum-pellyite. In addition, these synthesis experiments indicate that Fe-bearing pumpellyites crystallize at and are stable to lower temperatures than more aluminous pumpellyites—a result also consistent with natural systems.     

The high-pressure stability of zoisite and phase relationships of zoisite-bearing assemblages

The fluid-absent reaction 12 zoisite = 3 lawsonite + 7 grossular + 8 kyanite + 1 coesite was experimentally reversed in the model system CaO-Al₂O₃-SiO₂-H₂O (CASH) using a multi-anvil apparatus. The upper pressure stability limit for zoisite was found to extend to 5.0 GPa at 700 °C and to 6.6 GPa at 950 °C. Additional experiments both in the H₂O-SiO₂-saturated and in the H₂O-Al₂O₃-saturated portions of CASH provide further constraints on high pressure phase relationships of lawsonite, zoisite, grossular, kyanite, coesite, and an aqueous fluid. Consistency of the present experiments with the H₂O-saturated breakdown of lawsonite is demonstrated by thermodynamic analysis using linear programming techniques. Two sets of data consistent with databases of Berman (1988) and Holland and Powell (1990) were retrieved combining experimental phase relationships, calorimetric constraints, and recently measured elastic properties of solid phases. The best fits result in G _{f ,1,298} ^∘,zoisite=−6,499,400 J and S _1,298 ^∘,zoisite=302 J/K, and G _{f ,1,298} ^{∘,lawsonite}=−4,514,600 J and S _1,298 ^{∘,lawsonite}=220 J/K for the dataset of Holland and Powell, and G _{f ,1,298} ^∘,zoisite=−6,492,120 J and S _1,298 ^∘,zoisite=304 J/K, and G _{f ,1,298} ^{∘,lawsonite}=−4,513,000 J and S _1,298 ^{∘,lawsonite}= 218 J/K for the dataset of Berman. Examples of the usage of zoisite as a geohygrometer and as a geobarometer in rocks metamorphosed at eclogite facies conditions are worked, profiting from the thermodynamic properties retrieved here. Received: 23 December 1996 / Accepted: 29 August 1997     

Phase equilibria among pumpellyite,lawsonite, epidote and associated minerals in low grade metamorphic rocks

Phase relations of pumpellyite, epidote, lawsonite, CaCO₃, paragonite, actinolite, crossite and iron oxide are analysed on an Al-Ca-Fe³⁺ diagram in which all minerals are projected from quartz, albite or Jadeite, chlorite and fluid. Fe²⁺ and Mg are treated as a single component because variation in Fe²⁺/Mg has little effect on the stability of phases on the diagram. Comparison of assemblages in the Franciscan, Shuksan, Sanbagawa, New Caledonia, Southern Italian, and Otago metamorphic terranes reveals several reactions, useful for construction of a petrogenetic grid:

1. lawsonite+crossite + paragonite = epidote+chlorite + albite + quartz + H₂O
2. lawsonite + crossite = pumpellyite + epidote + chlorite + albite+ quartz + H₂O
3. crossite + pumpellyite + quartz = epidote + actinolite + albite + chlorite + H₂O
4. crossite + epidote + quartz = actinolite + hematite + albite + chlorite + H₂O
5. calcite + epidote + chlorite + quartz = pumpellyite + actinolite + H₂O + CO₂
6. pumpellyite + chlorite + quartz = epidote + actinolite + H₂O

     

一种长英黝帘石玉的岩石矿物学研究

采用X射线粉晶衍射、电子探针、化学分析法和傅立叶变换红外光谱等方法,对近来在北京珠宝市场上出现的一种粉白相间的玉石新品种进行了测试,全面分析了这种玉石的结构和成分,并根据硅酸盐体系的物质平衡原理,利用相混合计算(PMC)方法,估算了玉石中主要矿物的含量。结果表明,这种玉石中黝帘石含量占51.9%,钠长石占33.3%,石英14.4%,并含有少量的褐帘石、单斜辉石等矿物。样品中粉红色矿物的红外光谱最强峰位于1110～900cm-1范围内,为快速、方便地鉴定此种玉石提供了参考依据。