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![[Figure 1]](gj5202fig1mag.jpg)
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Figure 1
Arrangement of Si atoms in high and low quartz in different settings, using a right-hand coordinate system of axes. Heights are given as fractions of 100. In all cases the reference diad axis, as marked by an arrow, is chosen to be along x, 0, 0. The curved arrows indicate the direction in which the helices of Si atoms increase in height towards the observer. (a), (c) and (e) are for right (dextro) quartz, while (b), (d) and (f) are for left (laevo) quartz. (a) and (b) are for high quartz in space groups of type P6222 and P6422, respectively. (c) and (d) are in space groups of type P3221 and P3121, respectively, in the obverse setting. (e) and (f) are again in space groups of type P3221 and P3131, respectively, but in the reverse setting. r(+), r(−), z(+) and z(−) refer to the settings shown in Fig. 1 of Donnay & Le Page (1978  ). |
![[Figure 1]](gj5202fig1.jpg)
 | JOURNAL OF APPLIED CRYSTALLOGRAPHY |
ISSN: 1600-5767
