共查询到20条相似文献，搜索用时 62 毫秒
1.
The mechanical twinning of calcite is compared with ferroelastic behavior. For calcite a paraelastic prototype phase does
not exist, therefore a virtual prototype is defined with cubic m3m symmetry. Using this condition the strain tensors of all
domain states of mechanical twinning are calculated. With the use of the strain tensors, application of Sapriel's strain compatibility
law gives the crystallographic orientations of all possible twin planes between different domain states. The findings indicate
that the twin walls are {1 0 0} and {1 1 0} planes with respect to the morphological rhombohedral lattice. These twin plane
orientations from the equated strain tensors are in accordance with the r-and e-twin systems commonly observed in calcite.
Received: 17 December 1998 / Revised, accepted: 24 April 1999 相似文献
2.
Sector trilling of cordierite in hornfels in the inner part of a contact aureole at Daimonji, Japan is a new type which consists not only of six (100) sectors (a-sectors) forming trilling, but also of (001) sectors (c-sectors) and high-index sectors (h-sectors). Complex twins within and among these sectors were studied from a viewpoint of a pseudo twin. The complex texture originated from both growth and transformation processes. The c-sector consists of three groups of domains which are related by a pseudo twin. This intrasector pseudo twin indicates that the initial phase of the c-sector was hexagonal cordierite (indialite) which later transformed to orthorhombic. The a-sector is related to adjacent sectors by a rotation of 120° around the c axis, resulting in an intersector pseudo twin. The a-sector is interpreted to have formed by overgrowth of orthorhombic cordierite on prism faces of indialite. The h-sector with the dendritic texture is also interpreted to have grown as orthorhombic cordierite. In hornfels in the middle part of the aureole, cordierites with sector trilling often coexist with single crystals of cordierite, and the sector trilling has no c- and h-sectors. This trilling type suggests that nucleation of indialite was subsequently followed by growth of orthorhombic cordierite in its stable field. 相似文献
3.
Transformation Trillings in Cordierite 总被引：1，自引：0，他引：1
Cordierite sector trillings, which are found well developedin some A1-rich volcanic rocks and pelitic buchites, are thoughtto have formed initially as hexagonal high cordierite crystals.Subsequent ordering of the (Al, Si) configuration in the crystalstructure would have produced the present orthorhombic modificationand simultaneously the sector trilling, preserving in the processthe hexagonal habit of form. The predominance of the regularsixfold sector pattern in the composition plane configurationof the resulting trilling is best explained by assuming thatits formation is kinetically more advantageous than that ofother configurations because it mimics the hexagonal trend setby the initial crystal. The three orthorhombic orientations in the cordierite trillingshave parallel c-axes and each can be transformed into eitherof the other two by operation of a threefold axis (rotationthrough 120°) parallel to the common c-axis and coincidentwith the main axis of the original hexagonal form. The compositionplanes in the sector trilling pattern are shown to be essentiallyirregular in the present orthorhombic form; they do not belongto {110} or {130}. The traditional explanation that the trillings are multipletwins with repeated twin and composition planes of {110} or{130} is rejected since elementary geometrical considerationsshow that this model is only feasible if (110) (110) of orthorhombiccordierite equals 120°. X-ray work shows conclusively thatthis is not the case. In fact (110) (110) = 120° woulddefine a hexagonal symmetry. 相似文献
4.
J. Markgraaff 《Physics and Chemistry of Minerals》1986,13(2):102-112
Suitably oriented and cut strain gauged crystals of synthetic α quartz have been subjected to uniaxial compressive stress with the aid of a stiff, 2MN press. Complete axial and lateral strain versus stress curves were obtained during stress-induced Dauphiné twinning and eventual complete volumetric transition to the alternate structural state. The alternate twinned state as revealed by observed stress-strain curves, is attained by either a continuous domain wall movement or by a sudden intricate composite transition process after reaching a critical coercive stress. Lateral strain versus stress curves indicate that contraction occurs in two perpendicular directions during compression in two of the three orientations studied, and that a change in sign of the lateral strains usually accompanies the final transition to the alternate structural state. The order and the sign of observed lateral and axial strains before and after transformation, is confirmed by theory. The movement of twin domain walls is explained in terms of ferrobielasticity. The initial development of stripe-shaped Dauphiné twins requires stress concentrations between the contact surfaces of a crystal and the platens of the press. 相似文献
5.
The origin of sector trilling in cordierite is due to the hexagonal-orthorhombic Al, Si ordering transformation which under non-equilibrium conditions proceeds via a short-range ordered modulated structure. The growth of these distortion waves associated with progressive ordering produces a strain field which is minimized by a cyclic distribution of symmetrically equivalent modulations.Sector and complexly trilled cordierites in metamorphic rocks grew as the hexagonal polymorph with a considerable degree of Al, Si disorder. The enthalpy and entropy of disorder are evaluated from recent experimental work. The implication is that, in metamorphic rocks, substantial overstepping of stable equilibrium phase boundaries is required to nucleate hexagonal cordierite. Moreover, its composition coexisting with other phases will also be significantly different from that of the stable ordered form. 相似文献
6.
Domains of triclinic Na-feldspar which are a direct consequence of structural strain are investigated theoretically. The following conclusions are arrived at. Only two types of twin walls are created by spontaneous strain, namely the Albite- and Pericline twin walls. If intersections occur, rounded corners are predicted. Any third domain wall close to such an intersection must bend into an S-shape. Narrow domains between two twin walls tend to become needle-shaped close to the intersection with a further, perpendicular, twin wall. The combination of the elastic stiffness coefficients c 44 c 66-c 46 2 is expected to become small at temperatures near to the transition temperature. In the same temperature interval elastic fluctuations occur; their amplitudes and propagation directions are given. 相似文献
7.
G. Agrosì G. C. Capitani E. Scandale G. Tempesta 《Physics and Chemistry of Minerals》2011,38(2):101-109
Transmission Electron Microscopy (TEM) and High Resolution TEM (HRTEM) investigations were used to study a complex micro-structure
of twin-related lamellae of 15R SiC polytype, in syntactic coalescence with 6H-SiC. The analysis of the local stacking microstructure by means of HRTEM revealed that the perfect structure of 15R polytype, (23)3 was locally interrupted by numerous adjoining stacking faults parallel to (0001) with stacking of the coupled (22) and (33)
bilayers superimposed on the twin boundaries. HR images taken exactly across both the twin boundaries showed a zig-zag pattern
(23) that switched to (32) by a twin coherent interfaces or, alternatively, a zig-zag pattern (32) which passed to (23) through
an isolated (33), 6H like sequence. The selected area electron diffraction (SAED) patterns taken exactly above both the twin interfaces indicate
classifying of the twin found in this study as a “Friedelian” reticular merohedric twinning. However, two indistinguishable
twin operations matched the observed features: a reflection through rational plane (0001), and 180°-rotation around [0001].
Since individual Si and C atoms and even the SiC bilayer polarity could not be established from these HR images, the real
twin law was deduced by taking into account that the coherent structural match at the interface could be guaranteed only by
a 180°-rotation around [0001]. In order to explain the origin of the planar defects found in this sample, the growth mechanism
and the influence of the low-energy stacking faults were considered. 相似文献
8.
研究表明鞍山-本溪地区前寒武纪铁建造中的阳起石经受了褶皱或剪切变形作用,在相当于绿片岩相的温压条件下可形成波状消光,(001)裂理,扭折、机械双晶,重结晶等显微构造.由裂理及扭折带推导的一组滑移系为(001)[100],扭折造成的机械双晶具有S=0.57的剪切值,其双晶系统为(100)[001]. 相似文献
9.
Oxygen deficient perovskites in the system CaSiO3–CaAlO2.5 and implications for the Earth’s interior
U. W. Bläß F. Langenhorst D. J. Frost F. Seifert 《Physics and Chemistry of Minerals》2007,34(6):363-376
Oxygen deficient perovskites of the system CaSiO3–CaAlO2.5 have been synthesised at high-pressure and -temperature conditions relevant to the Earth’s transition zone in order to investigate
their stabilities in the Earth’s mantle and determine structural properties associated with vacancy incorporation. Two polysomes
of thermodynamically stable defect perovskites with Ca(Al0.4Si0.6)O2.8 and Ca(Al0.5Si0.5)O2.75 stoichiometry have been identified. The ordering of oxygen defects into pseudo-cubic (111) layers results in well-ordered
ten- or eightfold superstructures, respectively. At all other compositions examined, a metastable formation of perovskites
has been observed instead, which are assumed to grow initially disordered. These are now characterised by tiny domains, formed
due to subsequent ordering of vacancies along various pseudo-cubic {111} layers. Both ordered defect perovskites show a large
P–T stability field ranging from about 9–18 GPa and 4–12 GPa, respectively. Microstructural TEM analyses revealed the presence
of growth and ferroelastic twins, which indicate a phase transition from rhombohedral to monoclinic symmetry during quenching.
Electron energy loss spectroscopy of Si and Al K edges point at the presence of tetrahedral, octahedral and maybe some pentacoordinated silicon, whereas aluminium is predominantly
octahedrally coordinated with minor fractions in lower coordination. Observed properties are interpreted in terms of a new
structural model, explaining the observed phase transition and formation of different twin laws as well as giving reasons
for the development of such large superstructures. With respect to phase relations of the transition zone, the potential occurrence
of such defect perovskites in the Earth’s interior is discussed. 相似文献
10.
F. Wagner H. -R. Wenk H. Kern P. Van Houtte C. Esling 《Contributions to Mineralogy and Petrology》1982,80(2):132-139
Carbonate rocks deform preferentially by twin gliding on e={01ˉ18} and slip on r ={10ˉ14} and f={02ˉ21}. In polycrystalline aggregates strong textures develop. We report on experimentally produced textures in triaxial
plane strain geometry with orthorhombic symmetry at 200° C and 400° C. Pole figure of the experimentally deformed specimens
are compared quantitatively with theoretical simulations based on the Taylor theory using both slip and mechanical twinning
as mechanisms. Agreement at low and high temperature is satisfactory and documents that models developed for f.c.c. metals
can be applied to low symmetry minerals provided that deformation mechanisms are known and that mechanical twinning is properly
accounted for. Comparison with experimental results indicates that strain was nearly homogeneous at the conditions considered
and the same may apply to many geological textures. Three texture types are described which are differentiated mainly by the
relative importance of e twinning. 相似文献
11.
Transmission electron microscopy on natural calcium metatitanate perovskite (dysanalyte) reveals the following twin laws in the orthorhombic (space group Pbnm) phase: reflection twins on the {110} and {112} planes, and 90° rotation twins about the [001] axis (referred to as [001]90° twin). Single crystals that were heattreated and quenched from above 1585 K exhibit a dramatic change in domain structure compared with the starting material and specimens quenched from T < 1470=" k.=" mutually=" perpendicular=" {110}=" and=">90° twins are observed throughout the crystal, forming a cross-hatched domain texture. 1/2[001] antiphase domains, which are very rarely observed in the starting material, also become dominant in the crystal. This change in domain structure is interpreted as due to a structural phase transition in perovskite at a temperature below 1585 K. From the point symmetry elements that describe the twin laws and the translational elements that relate the antiphase domains, the most likely phase near 1585 K is tetragonal with space group P4/mbm. These results are consistent with high-temperature powder X-ray diffraction study. On the other hand, density of the {112} twins is increased significantly in the crystal quenched from 1673 K. Twin domains are either bound by mutually perpendicular {110} and (001) walls, or by {112} walls with {110} twin domains within the polygonal {112} domains. Both twin density variation and domain morphology suggest that the crystal may be cubic at this temperature. Microstructure of a single crystal deformed at 1273 K and 3.5 GPa (within the orthorhombic stability field) is morphologically quite distinct from that of the heat-treated specimens. Dislocations dominate the microstructure and often interact with twin domain boundaries.A National Science Foundation Science and Technology Center 相似文献
12.
J. W. Laughner T. W. Cline R. E. Newnham L. E. Cross 《Physics and Chemistry of Minerals》1979,4(2):129-137
Dauphiné (electrical) twins have been introduced into quartz crystals by means of suitably oriented mechanical stresses. Stress-induced twinning was observed optically by means of the photoelastic effect. Accompanying acoustic emission, first detected by ear, was quantitatively measured with a piezoelectric transducer and a suitable filtering and amplification system. Synchronized sound cinematography has been used to correlate the acoustic emission with visual observation of twinning. The resultant motion picture has been used to determine the stress levels required for twinning in Brazilian quartz and to set limits on the twin wall velocity. The possible relevance to rock noise and earthquake precursory phenomena is discussed. 相似文献
13.
Mechanical twins on both the Albite and Pericline laws are well developed on an optical scale in basic plagioclase from the Harris meta-anorthosite where the rock is affected by closely spaced shear fractures associated with pseudotachylite formation. In some cases the twinning is accompanied by kinking or intracrystalline fractures. The twins may be periodic and form a ladder structure and sometimes appear to intersect on an optical scale showing structures which very closely resemble those seen in microcline.Both Albite and Pericline twins are lenticular as observed by TEM, but isolated twin tips were rarely seen. No dislocations are associated with the twin tips. The twins in the optically observed ladder structure (when thicker than 2m), have themselves a very fine secondary ladder structure, consisting of periodic (200–600 nm) lenticular twins which impinge on the perpendicular twin wall. Intersecting twins were also observed and where two sets of equally thick twins intersect, M-twinning develops as shown by selected-area diffraction.The twin formation is analyzed in terms of the plagioclase structure and a coherent model for twin nucleation proposed. True twins can develop in plagioclase only if the Al/Si distribution is unchanged or nearly so after deformation. Mechanical twinning is quite easy in low plagio-clases between An100 and about An30 which have P¯1 or I¯1 lattices or domains with I¯1-type structures. Only one kind of nucleus can develop coherently in a single crystal, but it may grow to give either an Albite or a Pericline twin. Periodic nucleation and growth give complex textures. The qualitative variation of the twin energy as a function of the obliquity is given for different twin shapes and degrees of Al/Si order. M-twinning arises mechanically by coherent growth and interference of the strain fields. 相似文献
14.
Capturing strain localization in reinforced soils 总被引：2，自引：1，他引：1
Lade’s single hardening soil model with Cosserat rotation embodied in the finite element method is employed to investigate
the behavior of geosynthetic reinforced soils with special attention to the development of shear banding. The ability of the
finite element model to detect shear banding in a reinforced soil is examined against three high quality small-scale laboratory
plane strain tests on Toyoura sand with and without reinforcement. These three tests were chosen because of the clear failure
surfaces that developed in the soil during loading. The FEM analyses were able to reasonably simulate the plane strain laboratory
tests including both unreinforced and reinforced cases. The FEM analyses gave reasonably good agreement with the experimental
results in terms of global stress–strain relationships and shear band occurrences. Furthermore, and based on FE analyses of
a hypothetical geosynthetic reinforced soil (GRS) retaining wall, it is shown that the geosynthetic reinforcements are very
effective in hindering the formation of shear bands in GRS retaining walls when small spacing between the reinforcement layers
was used. When used properly, the geosynthetic reinforcements made the soil behave as a truly reinforced mass of considerable
stiffness and strength. 相似文献
15.
The time evolution of the Al, Si ordering and the ferroelastic distortion of the Mg-cordierite structure are quantified on a local length scale by Hard Mode Infrared Spectroscopy (HMIS). The line profiles of various absorption peaks were measured at room temperature and at 80 K. Their integrated intensities, frequencies and half width are correlated with the interacting order parameters Q od (Al, Si ordering), Q (displacive orthorhombic distortion) and their equivalent short-range analogs. It is shown that the phase transition between hexagonal and modulated cordierite is stepwise, as predicted earlier. The local structural state of quenched, modulated cordierite is essentially equivalent to that of the orthorhombic phase. A general concept is outlined which allows, in general, the independent determination of various interacting order parameters using HMIS. 相似文献
16.
The heat capacity of synthetic anhydrous Mg and Fe cordierite was measured by differential scanning calorimetry (DSC). Mg
cordierite was synthesized from a glass at high temperatures and shows an ordered structural state. Fe cordierite was synthesized
hydrothermally and dehydrated under reducing conditions to obtain H2O-free material. IR spectroscopy was used to ascertain the lack of H2O in both phases. The molar volume of both phases was measured using powder X-ray diffraction giving 23.316 (7) J/bar for
Mg cordierite and 23.672 (6) J/bar for Fe cordierite. DSC measurements between 300 and 950 K were made following the procedure
of Bosenick et al. (1996). The data show a precision of about 1% in the case of Mg cordierite and 1.5% for Fe cordierite.
Fitted Cp polynomials in J/mol/K are:
and
for Mg and Fe cordierite, respectively. The Cp values determined for Mg cordierite are slightly larger (1–3%) than those measured by drop calorimetry by Pankratz and Kelley
(1963). The Cp data for Fe cordierite permit the calculation of its standard third-law entropy, So
298 K from the reaction 3Fe cordierite=2 almandine + 4 sillimanite + 5 quartz giving 465 J/mol/K, which is in good agreement with
recent model estimates.
Received: 18 June 1999 / Accepted: 30 August 1999 相似文献
17.
S. Grassmann B. Cramer G. Delisle J. Messner J. Winsemann 《International Journal of Earth Sciences》2005,94(5-6):979-989
The geological history of Germany’s largest and most productive petroleum accumulation, the Mittelplate oil field in Schleswig-Holstein
(Northern Germany), is reconstructed by simulating the structural and thermal evolution along a 2D cross-section. The Mittelplate
field is located at the western flank of the Büsum salt dome at the transition from the Schleswig-Holstein mainland to the
German North Sea Sector. Organic geochemical data confirm the Lower Jurassic Posidonia Shale to be the predominant oil source
rock in the Schleswig-Holstein area. The studied section is characterized by salt walls and salt domes built up by Permian
evaporites. Reconstruction of the structural and thermal evolution of the Mittelplate field by means of basin modelling reveals
the dominating influence of salt dynamics on the entire petroleum system: The development of secondary rim-synclines during
salt rise provided accommodation space for the deposition of the Posidonia Shale as well as the deltaic Middle Jurassic reservoir
sandstones. The rise of the nearby Oldenswort salt wall controlled the timing of maturation and petroleum generation during
Cenozoic times. Hydrocarbon migration from the Posidonia Shale into the reservoirs occurred up-dip from the deeper subsiding
rim-syncline into the structural trap with the Middle Jurassic reservoir sandstones pinching out at the flank of the Büsum
salt dome. Along the modelled 2D section the field’s recent temperature field and its complex reservoir architecture are reconstructed. 相似文献
18.
A method of determining the number of Al-O-Al bonds per unit cell from 29Si nuclear magnetic resonance (NMR) data of synthetic cordierites with increasing Si, Al order is described. The number of Al-O-Al bonds is found to vary linearly with the logarithm of the annealing time. This may be correlated with previously published heat of solution data on similar samples (Carpenter et al. 1983) to determine the enthalpy change Δh, associated with a single Al?Si interchange in cordierite. Δh is found to be 8.1 kcal/mole. The NMR data show that the short range Al, Si order cannot be described in terms of twin domains of ordered orthorhombic cordierite. An ordering model derived from group theoretical constraints on possible Al, Si distributions within the hexagonal symmetry of the cordierite is found to provide a better fit to the NMR data. 相似文献
19.
20.
H.-R. Wenk M. Bortolotti N. Barton E. Oliver D. Brown 《Physics and Chemistry of Minerals》2007,34(9):599-607
Mechanical twinning in polycrystalline quartz was investigated in situ with time-of-flight neutron diffraction and a strain
diffractometer. Dauphiné twinning is highly temperature sensitive. It initiates at a macroscopic differential stress of 50–100 MPa
and, at 500°C, saturates at 400 MPa. From normalized diffraction intensities the patterns of preferred orientation (or texture)
can be inferred. They indicate a partial reversal of twinning during unloading. The remaining twins impose residual stresses
corresponding to elastic strains of 300–400 microstrain. Progressive twinning on loading and reversal during unloading, as
well as the temperature dependence, can be reproduced with finite element model simulations. 相似文献