Sulphate of Lime
- Div. 1. Crystallized.
The situations in which substances are found are not only geologically instructive, but chemically:—thus the present specimen answers many purposes. Gypsum, as I have before mentioned, is rather peculiar in certain places in the form of its crystallization. There are two or three varieties included in this example: the most remarkable is the large one, which is rather a rough and thick specimen, and conforms to the outline below. Such is sometimes found among the many varieties at Shotover Hill, Oxfordshire. It is beginning to form a flat apex by roundish faces on the acute angle, part of the first advance towards the peculiar lenticular crystal, one of the rarest of this substance—(of which hereafter). It is of a pretty pink colour in the upper specimen, not common to Hyaline Gypsum. It is peculiarly situated, being suspended and supported by other crystals, and again supporting Carbonate of Lime in whole metastatic crystals, and also Quartz. See figs. 1 and 2. Now it has happened that Carbonate of Lime, such as these figured (of which I have specimens), and Quartz crystallized on all sides in great numbers, loose and independent of each other, have been found included in these nodules*, which are impervious to water. The query then is. Could they be formed included in the Sulphate of Lime, and the latter become dissolved again by water, and evaporate previous to the covering (which is partly Agate lined with Quartz crystals) becoming imperviable? or, Could any thing else have held them in solution, so that they might become so independent as to seem as if they were put in in separate crystals?
The two lower figures, are examples of the flattened apex, and its tendency towards another figure, showing the opposite ends, and the curious manner in which the crystals mix while forming, and yet show a constant tendency in its progress from its usual shape to that of a new appearance, by little else than the loss of the column.
- * Of which my friend Mr. Johnson of Bristol has specimens.