Kinematics of experimentally produced deformation bands in stibnite

Using videotape techniques, we have observed the kinematic development of a variety of microstructures during experimental deformation of single crystals of stibnite (Sb2S3). The crystals were deformed by flexure or uniaxial compression at room P-T conditions in a small strain device attached to the stage of a reflecting microscope. In more than 50 experimental runs, the primary microstructures produced in stibnite were deformation bands, not deformation twins as often reported in the literature. Translation gliding along (010) [001] results in visible slipbands and produces two basic types of deformation bands, each with a variety of subtypes. Kink bands form with [phi] (angle of internal rotation) [approximate, equal]70[deg] and perpendicular bands develop with [phi][approximate, equal] 90[deg]. Other optical deformation features seen forming were: breccia fragments, bent and opened cleavages, and microfolds.Four stages could be seen in the kinematic development of deformation bands. During initiation, bands form by nearly instantaneous propagation of a narrow bent zone across the crystal. During later migration, the bands widen at a rate invariably slower than the rate of initiation. Termination of bands occurs when growth is impeded by intersections with grain boundaries or other deformation features. During late modification, previously formed bands with straight boundaries are sheared, bent, and compressed. Unconfined crystals tend to form kinks, whereas the perpendicular bands formed in samples confined in relatively rigid plastic. Naturally deformed stibnites show the same features. Television photomicroscopy has great potential for studying microstructures during deformation.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23215/1/0000144.pd

CRYSTAL-STRUCTURE OF PREHNITE FROM KOMIZA

The criystal structure of prehnite (Ca2(Al,Fe) (OH)2 [ Si3AlO10])from Komi\u17ea (Yugoslavia) has been refined in the space group P2cm (a=4,646(2) \u1fa, b= 5.491(3) \u1fa, c=18.52(3) \u1fa, Z=2). Si and Al showed a completely ordered distribution in the structure. The obtained Fe-Alsubstitution for the octahedral coordination is 17%. No monoclinic domains could be observed in the crystals. Laue photographs show that the splitting of the diffraction maxima in prehnite from Komi\u17ea is due to lattice rotation around the direction of the b axis

Authigenic mica in Early Miocene volcaniclastic rocks of the Macelj area, Hrvatsko Zagorje, Croatia

In the Early Miocene zeolitized volcanicalstic rocks from NW part of Hrvatsko zagorje green authigenic mica occurs in thin veins and coatings of glass shard vesicles. X-ray powder pattern with widened but still relatively sharp reflections is characteristic for 1M micas, with Fe-rich octahedral sheet. The observed value d(060) is 1.508 \uc5. IR spectrum is characterized by sharp absorption bands in the OH stretching region, with two strongest bands at 3580 cm-1 and 3600 cm-1 ascribed to Al-Fe3+ and Al-Mg cationic environment of the OH groups. Microprobe analyses revealed that this is an interlayer-deficient dioctahedral mica, with Al as dominant cation in octahedral sheet, viM3+>1.2, and low tetrahedral substitution, with quite peculiar chemical composition that does not correspond ideally to any member of the mica group