X-ray study of Brazil twins in natural amethyst

Abstract

The physical state of the crystal lattice is determined of an unprocessed, natural rhombohedra1 growth face, r (OIll), of amethyst quartz having well expressed lamellae structure. By applying the X-ray diffraction methods: double crystal spectrometry (topographs), reflection X-ray topography in divergent beam, as well as polarizing optical microscopy the lamellar structure is found due to Brazil twins present. Especially a determination is made of the lattice spacing fluctuations and lattice rotation over the areas in which the lamellae outcrop on the natural face. I n addition, detailed studies of the concentration of some impurities a t the twin boundaries are performed using the quantitative EPMA analysis. They indicate that in the case under discussion the distorted lattice around the twin boundaries is caused not by the impurities, but most probably by plastic flow or by migration of vacancies to the boundary.Es wird der physikalische Zustand des Kristallgitters einer unbehandelten, naturlichen rhomboedrischen Wachstumsflliche r (0111) eines Amethystquarzes mit gutausgebildeter Lamellarstruktur bestimmt. Mit Anwendung von Rontgenbeugungsmethoden: Doppelkristallspektrometrie (Topographien), Reflexions-Rontgen-Topographie im divergenten Strahl sowie mit optischer Polarisationsmikroskopie wird gefunden, daB die Lamellarstruktur auf vorhandene Brasilzwillinge zuriickzufiihren ist. Insbesondere werden die Gitterkonstantenfluktuationen und Gitterdrehung iiber den Flachen in denen die Lamellen an der natiirlichen Fliiche austreten, ngher bestimmt. ZusLtzlich werden ausfuhrliche Untersuchungen der Konzentration einiger Storstellen an den Zwillingsgrenzen mittels quantitativer EPMA-Analyse durchgefiihrt. Sie zeigen, daB fur den diskutierten Pall das gestorte Kristallgitter um die Zwillingsgrenzen nicht von den Storstellen, sondern hochstwahrscheinlich dnrch plastisches FlieBen oder Wanderung von Leerstellen zur Grenze verursacht werden.

Redetermination of the structure of caesium hydrogensulfate

“…It turns out that the low-temperature structure of CsHSO4 has no analogue among the AHBOa-type structures, i.e. CsDSO4 (Merinov, Baranov, Maksimov & Shuvalov, 1986), CsHSeO4 (Baran & Lis, 1987), CsHI-xDxSO4 (x = 0.67) and CsHl-xDxSeO4 (x=0"70) (Balagurov, Beskrovnyi, Savenko, Berinov, Dlouha, Vratislav & Jirak, 1987) together with RbHSO4 (Ashmore & Petch, 1975), NHaHSO4 (Nelmes, 1972), NaHSO4 and KHSO4 (Sonnevelt & Visser, 1978), and is rather similar to the paraelectric structure of CsH2PO4 (Matsunaga, Itoh & Nakamura, 1980) apart from an H atom which combines O(1) and 0(2) in the case of CsH2PO4. Although the shape of SO 4 is fairly regular, we find that the bond lengths S---O(3) and S--O(4) are a little longer than S---O(1) and S---O(2) as shown in Table 2.…”

Phase transitions in N(CH3)4HSO4: a novel compound with an incommensurate phase

“…Another compound with formula, CsHSeO4, also shows as well (Baranov, therefore seems that proton conductivity in the crystal struca similar empirical a superionic phase (Baranov et al, 1982). Its crystal structure consists of isolated Cs atoms and of chains of hydrogen-bonded selenate ions (Baran & Lis, 1987).…”