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IV. On the Formation of Chalcedony

  • G. S. Mackenzie

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Although I possess a collection of specimens of Chalcedony, made expressly with the view to enable me to form some plausible theory of its formation; and; although my cabinet contains a variety of forms, perhaps unequalled in any other collection, I have, for many years, refrained from describing them, because the oftener I contemplated my specimens, the less able I found myself to apply any single agent, so that its operations alone could account for their forms. It is, indeed, very long since I entertained the opinion, that no hypothesis founded on the separate agency of heat or of water, could be satisfactory to speculative minds; and that geologists could never account for the formation of individual minerals, or of the rocks containing them, without combining the power of heat with that of water. But even this combination, though it can be easily conceived capable of forming many of the productions of the mineral kingdom, leaves numerous phenomena unexplained.

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page 86 note * I have but one specimen in which I cannot distinguish the agate forms even with the help of polishing.

page 87 note * This Memoir is printed nearly as it was read to the Society; and there is unquestionably some awkwardness in the references to the specimens, while neither specimens nor drawings of them can be examined. With respect to drawings, it is exceedingly difficult to represent mineral bodies well, without great labour.and expence; and the forms of the specimens referred to in this Memoir, as well as their general appearance, are such as render an attempt to represent them by engraving almost hopeless. Indeed it would be useless, as many of the specimens referred to can be viewed only by turning them in different directions, and placing them in different lights. The facts are stated in such a manner, as, it is hoped, will leave nothing equivocal in the mind of the reader.

page 91 note * Among numerous examples, well known to mineralogists, I may mention one specimen in my possession, not much larger than a man's fist, which is formed of distinct crystals of brown quartz, white topaz, and beryl.

IV. On the Formation of Chalcedony

  • G. S. Mackenzie

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