Kristallstrukturverfeinerung und reflexionsmessungen am Hausmannit, Mn3O4
Zusammenfassung Die Kristallstruktur eines Hausmannits von Langbån, Schweden, wurde an Hand von 462 unabhängigen Einkristall-Röntgendiffraktometerdaten zu einemR = 0.036 (R w = 0.034) verfeinert. Die Jahn-Teller-Verzerrung des Mn3+O6-Oktaeders ist relativ stark: Mn3--O = 1.930 (1) Å (4 x); 2.282 (1) Å (2 x), und die Anisotropien der thermischen Schwingungen von Mn3 und O unterscheiden sich deutlich von denen analoger Atome in kubischen Spinellen. Es wird gezeigt, daß aus einer stereochemischen Sicht der Strukturtyp des Hausmannits nicht die einzig geometrisch mögliche JahnTeller-Verzerrung des Spinell-Typs ist. Das Reflexionsvermögen des Hausmannits wurde an einer orientiert geschnittenen Platte mit polarisiertem Licht ( = 400–700 nm) in Luft und in Ölimmersion gemessen und Brechungsindizes und Absorptionskoeffizienten wurden bestimmt.
With 2 Figures 相似文献
T°C 相似文献
14.
The polarized (E‖a′, E‖b and E‖c) electronic absorption spectra of five natural chromium-containing clinopyroxenes with compositions close to chromdiopside, omphacite, ureyite-jadeite (12.8% Cr2O3), jadeite, and spodumene (hiddenite) were studied. The polarization dependence of the intensities of the Cr3+ bands in the clinopyroxene spectra cannot be explained by the selection rules for the point groups C 2 or C 2v but can be accounted for satisfactorily with the help of the higher order pseudosymmetry model, i.e. with selection rules for the point symmetry group C 3v. The trigonal axis of the pseudosymmetry crystal field forms an angle of 20.5° with the crystallographic direction c in the (010) plane. D q increases from diopside (1542 cm?1) through omphacite (1552 cm?1), jadeite (1574 cm?1) to spodumene (1592 cm?1). The parameter B which is a measure of covalency for Cr3+-O bonds at M1 sites in clinopyroxene depends on the Cr3+ concentration and the cations at M2 sites. 相似文献
15.
A. Dal Negro S. Carbonin C. Domeneghetti G. M. Molin A. Cundari E. M. Piccirillo 《Contributions to Mineralogy and Petrology》1984,86(3):221-229
A clinopyroxene suite from lherzolite inclusions associated with the Victorian (Australia) “Newer Volcanics” has been investigated
with the aim of understanding the clinopyroxene crystal-chemical response to increasing temperature (e.g. a melting model
and/or crystallization processes prevailing at high pressure).
The M1 clinopyroxene polyhedron dominates the intracrystalline physical-chemical variations, essentially given by the triple
substitution AlVIFe
M1
2
Ti4+⇌Cr3+ Fe3+Mg
M1
2+
corresponding to an increase in the volume of M1 with increasing Mg/Mg+Fe2+ (mg) for the clinopyroxene. A relative Ca2+ increase in M2 ensures the necessary charge balance. However, Na+ occupancy of M2 persists to the highest mg values, i.e. maximum thermal stability, where the volume of M2 is the largest due to Fe
M2
2+
depletion. The variations of M1 and M2 volumes are greater than, and opposite to, the variations in the volume of T (tetrahedron)
by factors of ca. 3 and 1.5, respectively. Inclusions with relatively low clinopyroxene content (Mt. Porndon specimens) show
distinct intracrystalline variations, essentially reflecting lower AlVI, i.e. higher volume of M1, and implying a lower pressure regime compared to clinopyroxene-rich analogues (Mt. Leura specimens).
The intracrystalline relationships of the Mt. Porndon clinopyroxene suggest that the host peridotite inclusions survived larger
degree of mantle melting at shallower depths relative to the Leura analogues. 相似文献
16.
Tsuneaki Goto Thomas J. Ahrens George R. Rossman 《Physics and Chemistry of Minerals》1979,4(3):253-263
Unpolarized absorption spectra of single crystals of Cr3+ doped Al2O3 (synthetic ruby) have measured using a new, time-resolving, dispersive, streak photographic system over the range ~350 to ~700 nm during a series of shock loading experiments. The crystal field absorptions assigned to the transition 4 A 2g→4 T 2g were observed to shift in a series of experiments from 555±1 nm at atmospheric pressure to 503±5 nm at 46 GPa. In a single experiment at 32 GPa the 4 A 2g→4 T 1g transition was observed to shift from 405±1 to 386±5 nm. The present data extrapolate downwards in compression toward the 10 GPa data of Stephens and Drickamer (1961) although both crystal field absorption energies increase considerably less with compression than predicted by the simple ionic point charge model. The single datum observed for the Racah parameter B, 588±38 cm?1 at 32 GPa, is consistant with previous results to 10 GPa and the trend of decreasing B, with compression expected from the divergence of the data from the point charge model due to increasing covalancy. 相似文献
17.
Polarized optical absorption spectra of Mn(IV) in octahedral crystal fields of Mn(SeO3)2 have been studied by means of microscope-spectrometry in the range 40000-4000 cm?1 and at temperatures between 113 K and 293 K. Intense charge-transfer absorptions (linear absorption coefficient α ? 30000 cm?1) completely mask the d-d transitions in the UV and VIS region above ≈23000 cm?1. The optical electronegativity χ opt of Mn(IV) in Mn(SeO3)2 is estimated to be 2.7. In accordance with the d 3 configuration of tetravalent manganese three d-d bands observed at ambient temperatures at 13250, 14137 (α≈50 cm?1) and ≈18500 cm?1 (α≈500–800 cm?1) are assigned to the spin forbidden 4 A 2g →2 E g and 4 A 2g →2 T 1g transitions as well as to the first spin allowed 4 A 2g →4 T 2g transition, respectively. These assignments allow the calculation of the following ligand field parameters: Dq ≈ 1850 cm?1, B 55 = 869 cm?1 (β 55 = 0.82), and C = 2346 cm?1 (293 K). 相似文献
18.
Miscibility and compatibility of braunite,Mn2+Mn
6
3+
O8/SiO4, in the system Mn-Si-O at 1 atm in air
Irmgard Abs-Wurmbach 《Contributions to Mineralogy and Petrology》1980,71(4):393-399
Experimental investigations between 800 ° to 1,100 ° C yielded no evidence for extensive substitution of Mn2++Si4+2Mn3+ in braunite, leading to a complete solid solution series between partridgeite (Mn2O3) and braunites with silica contents up to 40 wt. % as proposed by Muan (1959a, b). In the presence of excess manganese braunite of nearly ideal composition coexists at 800 ° C with partridgeite and at T1,000 ° C with hausmannite (Mn3O4). At 800 ° C and 1,000 ° C braunite coexists, in the presence of excess silica, with a SiO2-polymorph and at 1,100 ° C with rhodonite (MnSiO3). Quantitative analysis of the X-ray patterns of coexisting cristobalite and braunite confirms a maximum silica-excess in braunite of only about 2 wt.% over the ideal composition, Mn2+Mn
6
3+
SiO12. 相似文献
19.
雷州英峰岭玄武岩中单斜辉石巨晶的地球化学和地幔交代作用 总被引:5,自引:1,他引:5
雷州半岛英峰岭火山岩中单斜辉石巨晶以低Mg^#值(0.62—0.47)、贫重稀土(HREE)和富Al2O3、TiO2、Na2O和中稀土(MREE)为特征,并具有明显的成分变化。随着Mg^#降低,单斜辉石的Al:O,(11.58~6.97%,)、TiO,(2.28~1.06%)和HREE逐渐降低。这种变化特征不同于世界上大多数辉石巨晶的变化规律。随着演化辉石巨晶的大多数不相容元素,如Nb、Sr、Zr、Hf和LREE—MREE逐渐增加。低的Mg^#值和Ni、Co、Cr含量指示巨晶母岩浆是一种强烈演化的残余岩浆(Mg^#=0.27~0.35)。分离结晶模拟表明本研究最富镁的巨晶(Lz-54)的母岩浆很可能是由拉斑玄武质岩浆经70~80%,以单斜辉石为主的结晶分异后形成。而本研究的其它辉石巨晶是该母岩浆在不同演化阶段(25~80%)分离结晶的产物。分离矿物中除了单斜辉石还包含了大量的石榴子石、斜长石和钛铁矿。温压计算表明英峰岭巨晶是高温岩浆在56~60km深的上地幔的结晶产物(r=1290℃~1130℃,P=1.73~1.83GPa),这一深度有利于石榴子石结晶。对比不同地区辉石巨晶的成分特征和形成条件,作者指出不同地区单斜辉石巨晶各种元素的不同变化规律主要受母岩浆成分和结晶条件控制。巨晶母岩浆在地幔结晶时对围岩橄榄岩进行了不同程度的交代作用。早期贫流体的岩浆对橄榄岩的交代作用较弱,只有Sr,La等强活动性元素被明显改变;晚期富流体(F,P,H2O)岩浆对橄榄岩的交代作用强烈,大多数元素被明显改变。因此,可以推断交代熔体中流体的含量是影响地幔橄榄岩交代作用的关键。 相似文献
20.
The effect of Ca-Tschermaks component on trace element partitioning between clinopyroxene and silicate melt 总被引:19,自引:0,他引:19
We have studied the influence of Ca-Tschermaks (Calcium Tschermaks or CaTs) content of clinopyroxene on the partitioning of trace elements between this phase and silicate melt at fixed temperature and pressure. Ion probe analyses of experiments carried out in the system Na2O–CaO–MgO–Al2O3–SiO2, at 0.1 MPa and 1218°C, produced crystal-melt partition coefficients (D) of 36 trace elements (Li, Cl, Sc, Ti, V, Cr, Fe, Co, Ge, Sr, Y, Zr, Nb, Mo, Ru, Rh, In, Sn, Sb, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta and W), for clinopyroxene compositions between 10 and 32 mol% CaTs. Partition coefficients for 2+ to 5+ cations show, for each charge, a near parabolic dependence of log D on ionic radius of the substituting cation, for partitioning into both the M1 and M2 sites of clinopyroxene. Fitting the results to the elastic strain model of Blundy and Wood [Blundy, J.D., Wood, B.J., 1994. Prediction of crystal-melt partition coefficients from elastic moduli. Nature 372, 452–454] we obtain results for the strain-free partition coefficients of theoretical cations (D0), with site radius r0, and for the site's Young's Modulus (E).
In agreement with earlier data our results show that increasing ivAl concentration in cpx is matched by increasing D, EM1, EM2 and D0 for tri-, tetra- and pentavalent cations. The degree of fractionation between chemically similar elements (i.e. Ta/Nb, Zr/Hf) also increases. In contrast, D values for mono-, di- and hexavalent cations decrease with increasing ivAl in the cpx. The large suite of trace elements used has allowed us to study the effects of cation charge on D0, r0 and E. We have found that D0 and r0 decrease with increasing cation charge, e.g. r0=0.66 Å for 4+ cations and 0.59 Å for 5+ cations substituting into M1. Values of EM1 and EM2 increase with cation charge as well as with increasing ivAl content. The increase in EM2 is linear and close to the trend set by Hazen and Finger [Hazen, R.M., Finger, L.W., 1979. Bulk modulus-volume relationship for cation–anion polyhedra. J. Geophys. Res. 84 (10) 6723–6728] for oxides. EM1 values are much higher and do not fit the trend predicted by the Hazen and Finger relationship. 相似文献 |
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