As is well known, quartz rarely shows well-defined cleavages. Kenngott has shown that quartz that has suddenly been cooled, after strong heating, has a tendency to break up in the directions of rhombohedron faces. Breithaupt (cf. Hintze, Min., 1904, vol. 1, p. 1273) mentions ‘cleavage following the primary rhombohedron and the prism, rarely well defined, often passing into conchoidal fracture’.

It may be useful to put on record an example of clear rock-crystal in which cleavage is developed in all three 60° directions of the prism faces. The specimen was originally in the Daimeries collection, in Brussels, having been bought years ago at Idar, near Oberstein on the Nahe, by A. Daimeries. I obtained it from Mr. A. G. F. Gregory, who had bought the Daimeries collection. The locality from which it came is, unfortunately, unknown.