Mizuhiko Akizuki

Plastic deformation of quartz at room temperature: A Vickers Nano‐Indentation Test

Vickers indentation tests of natural quartz were performed with a load of 98 mN at room temperature and one atmosphere. Atomic force microscopy revealed no evidence of fracturing during indentation. Transmission electron microscope observations indicate that no dislocations were generated during the indentation tests. However, high resolution electron microscopy revealed that sharp creases of crystal lattices had developed. These observations lead to the conclusion that quartz deformed plastically even at room temperature. The plastic strain was accommodated by the mechanism of lattice creasing, which is described here for the first time.

Triclinic liddicoatite and elbaite in growth sectors of tourmaline from Madagascar

Abstract Crystals of liddicoatite-elbaite tourmaline from a pegmatite in Jochy, Madagascar are composed of o{021̄1}, r{101̄1}, c{0001}, a{112̄̄0}, and m{101̄0} sectors, which correspond to the prominent crystal faces, respectively. Therefore, the sectors were produced during growth, not by strain after growth. The o, m, and r sectors of one specimen are biaxial between crossed polars [2V(-) = 30°, 20°, and 15°, respectively] and triclinic, as indicated by X-ray diffraction. The a sector is optically biaxial and orthorhombic. The c sector is optically uniaxial and essentially trigonal as indicated by single-crystal X-ray diffraction. The o, r, and c sectors are of liddicoatite component, whereas the a sector of the one specimen corresponds to fluor-elbaite. Another crystal specimen comprises a and m sectors, which are polysynthetically twinned, resulting in striations parallel to the c axis on the prism faces, and of liddicoatite. All five sectors have vacancies in the X-site (Ca, Na, ⃞ ).

Optical properties and crystal structure of triclinic growth sectors in vesuvianite

Abstract Sectored vesuvianite showing optically triclinic properties was studied by X-ray and P-FTIR analyses, and the origins of the internal optical texture are discussed. A monoclinic refinement (space group P2/n) suggests that site occupancies are slightly different among the Al(2) series, though the OH− dipole is randomly oriented in all sectors. A relationship between the surface and internal texture suggests that these sectoral structures were produced during crystal growth, not by phase transitions.

Lamellar texture and optical anomaly in andradite from the Kamaishi mine, Japan

Detailed investigations of optical anomalies and surface texture of birefringent grossular-andradite from Kamaishi mine, Japan, were made by optical polarizing microscopy, electron-probe microanalysis (EPMA) and back-scattered electron imaging from the standpoint of crystal growth. This garnet shows one-to-one correlation between surface features and the internal texture. The average chemical composition measured by EPMA near rim is Adr 78.6 Grs 21.1 Sps 0.2 and near core is Adr 57.0 Grs 42.2 Sps 0.7 . The surface features correspond to internal texture observed under crossed polarizers. The triangular sectors in rhombic blocks under cross polarizers are symmetric with [001] axis and show sector twins. Scanning electron microscopy (SEM) showed a pyramidal shape of rhombohedral growth hillocks consistent with spiral growth mechanism. The vicinal faces of blocks show extinction angles of 31–40° with respect to the crystallographic direction [001]. This andradite is optically biaxial with 2V z of about (−) 70° in both {110} sectors. The principal direction X is almost normal to (110) and coincides with the growth direction [110]. The positions of Y and Z rotate by up to 19° from the crystallographic direction [001] and [110] respectively, around X . The value of X varies slightly from sector to sector; however, a 2-fold axis is parallel to [110]. The symmetry determined optically for the garnet is monoclinic or triclinic.

Origin of optical variation in chabazite

At a low degree of supersaturation a crystal forming from solution grows by repeated addition of layers to the crystal faces. A three-dimensional structure is therefore formed by the stacking of two-dimensional nets. The two-dimensional atomic arrangement exposed on the growing faces and its symmetry controls the ordering of cations and/or anions added to the surface. The distribution of Al and Si seems to be particularly prone to ordering of this kind. In chabazite the optical properties corresponding to the degree of ordering differ from growth sector to growth sector produced on the vicinal faces {hkill} of growth hillocks. The optically triclinic sectors in chabazite form on a vicinal face which inclines to the morphological mirror plane and the c-axis, and the mirror plane of the growth hillock becomes the twin plane of the sector. Thus, chabazite showing rhombohedral form consists of six twinned sectors corresponding to six {10ulbar;11} faces in which some small twinned sectors correlated with the symmetrical vicinal faces can be seen under the optical microscope.

Origin of low-symmetry growth sectors in edingtonite and yugawaralite, and crystal structure of the k{011} and v{120} sectors of yugawaralite

Abstract Edingtonite and yugawaralite showing sectoral textures were studied by polarized optical microscopy and X-ray analysis. In edingtonite, the m {110} sector (2Vα = 22°) is optically triclinic and the c {001} sector (2Vα = 52°) is orthorhombic. In yugawaralite, the k {011} sector is optically monoclinic, whereas the v {120} sector is triclinic. Their crystal structures were determined. The results of refinement showed that the space groups of the k {011} (Rw = 4.5%) and v {120} (Rw = 5.1%) growth sectors are monoclinic Pc and triclinic P1, respectively. In the v {120} sector, several interatomic distances, bond angles and site occupancies are different with respect to a symmetrical plane of the structure, and therefore the monoclinic c glide is extinct. Thus, the X-ray symmetry correlates with the optical one. From the relationship between the surface and internal texture, the symmetry and sector can be explained by cation (Al/Si) ordering during non-equilibrium crystal growth.

Crystal structures of the {011}, {610}, and {010} growth sectors in brewsterite

Abstract Crystal structures were determined by single-crystal X-ray methods for the {011}, {610}, and {010} growth sectors of brewsterite from Strontian, Scotland. Refinements Rw = 4.3-6.6%) showed that all three growth sectors are triclinic and that their structures differ slightly.

An electron microscopic study of anorthoclase spherulites

Abstract Spherulites consisting of fibrous alkali feldspar and silica minerals are produced by devitrification of rhyolite glass under hydrothermal conditions. The alkali feldspars (Ab 72.5 Or 23.0 An 4.5 , Ab 81.7 Or 14.0 An 4.3 ) in spherulites from two localities in Japan consist of triclinic anorthoclase showing fine cross-hatched twinning and monoclinic sanidine showing fine cross-hatching not attributable to twinning. The cross-hatching, which corresponds to albite and pericline twinning, is produced in the process of transition from a monoclinic to a triclinic phase. The spherulite may develop at a temperature lower than about 200°C because the co-existing silica mineral is not quartz, but metastable tridymite. According to the phase diagram of the alkali feldspars by MacKenzie (1952), the alkali feldspars should have been triclinic during growth. However, the textures show that the alkali feldspar grew as a disordered monoclinic phase. Because of the high growth rate, the Al/Si disordered structure was produced during growth and afterwards transformed into a triclinic structure with cross-hatched twinning.

The lamellar structure in moonstone and anorthoclase from Korea

Moonstone and anorthoclase from Korea were investigated using electron microscope. Lamellae of moonstone were in the range of 1,200 to 3,000 Å, and anorthoclase have fine lamellae ranging from 20 to 900 Å. The outer part of every specimen has exsolved more perfectly, and the lamellae are coarse. The inner part is in the process of exsolution, and the lamellae are extremely fine. The lamellae are parallel to (¯801), and the streations on diffraction spots are oriented normal to the lamellae.

Fractured Surface of Opal

Fine parallel lines were found on fractured surface of opal under reflection optical microscope. Study of replication electron microscopy of fractured surface with fine lines revealed three distinctive patterns. These were (1) lamellae with voids and without voids, (2) lamellae with two kinds of voids, and (3) lamellae without voids.