- 鉱物学雜誌 (ISSN:04541146)
- vol.3, no.6, pp.543-556_4, 1958-09-30 (Released:2010-02-08)
On the basal plane of one crystal of hematite from an andesitic lava at Ayumikotan, Japan, three types of growth pyramids are described.First type, which is called the “tetrahedral” growth pyramid, consists of many closely spaced, thin, concentric, equi-lateral triangular growth layers. (Photo. 2, 5) On some of these growth pyramids spiral growth and interlacing can be observed. (Photo 5 a, b) On some growth pyramids the layers on one side of the triangular are produced into a peak suggesting the presence of an imperfect screw dislocation. (Photo. 5a) Measurement by multiple beam interferometry (Photo. 4) and fringes of equal chromatic order (Photo.3) show that thinnest growth layrs are 2.3Å thick (I/6 of the unit cell). Further details may be seen in Table 1.Second type is called the “triangular” growth layer. They are equi-lateral triangular growth layers on which no spirals have been observed. (Photo.7) It is suggested that growth took place by two-dimensional neucleation. The origin of the structure within the triangles and the linear arrangement of growth centres is described in the paper. (Photo.8, 9) At some distance from the growth triangles, a serrated structure, like sow-teeth, is developed. (Photo.6) This may also be seen around all growth pyramids of the first type. Measurements of thickness are shown in Table 3.In the third type of growth pyramids (Photo.10, 11) the thickness of the layersin different cases varies from 1 to 4 unit cell including thickness of 2n+1/2 unit cell (see Table4). These growth pyramids seem to be formed by screw dislocation, as there is a pit at the centre of each growth pyramid. The type of interlacing shown by these growth pyramids (Photo.11) suggests that polytypism may be present.From these observations it is deduced that this crystal has grown under the condition of comparatively high supersaturation.