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X.—Chapters on the Mineralogy of Scotland. Chapter Second.—The Felspars. Part I

Published online by Cambridge University Press:  14 March 2016

Heddle
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Extract

Before submitting the results of my examination of the silicates, it is incumbent upon me to give an outline of the processes adopted for their analysis, seeing that the amount of confidence which is to be placed in the results must rest very immediately thereupon.

1. Determination of the Water. — In all silicates which were found, after thorough drying, to give out moisture when heated in the closed tube, the amount of loss upon ignition was calculated as water. About 2 grammes, crushed in the diamond mortar, were first merely heated throughout in the air-chamber of a water-bath, the contact temperature of which was 212° Fahr., the temperature of the air-space being never below 199°. The weight after this heating was taken; and, except in the case of a mineral functioning in any peculiar way, the loss in weight was estimated as hygroscopic moisture. The mineral was now continuously heated in the bath until the weight was found to be constant. It was then exposed for the space of one hour to a full red heat, in the flame of a Bunsen burner, after which it was re-weighed. Finally, it was exposed for ten minutes to a heat approaching whiteness, in a three-jet Griffin blast-furnace, again re-weighed, and again heated in this furnace, until the weight was constant.

Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 28 , Issue 1 , 1877 , pp. 197 - 271
Copyright
Copyright © Royal Society of Edinburgh 1876

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References

page 197 note * I cannot too highly recommend this simple and cheap little furnace; it commands every temperature, and, for mineral analysis, is superior to all others which require a blowing apparatus.

page 203 note * I except, of course the case where titanic acid is present.

page 217 note * Or Saponite or Strigovite;—not yet analysed.

page 229 note * Were it not so, we would have to regard these as being all microlines; but DESCLOISEAUX (Comptes rendus, April 17, 1876,) holds these to consist of a mixture of orthoclase, microlin, and albite. In perthite,—where there is a somewhat parallel banding of orthoclase and albite,—the two were probably paragenetic in time; but the microscopic structure of perthite—the only mineral in which there has been a chemical determination of the nature of the layers—is so different from this, as to form the very strongest arugment against the view that the intruded material is here albite.

page 233 note * Supposing the crustal to be positioned as usual with the faces m vertical.

page 234 note * This consisted of a single crystal of nearly an inch in size, imbedded in granite—or part of a granitic vein,—it was found and given to me by the late T. Bell of Ballgrogan. The precise locality has escaped my memory. It has a pale but fine green colour.

page 240 note * Fe2O, also 08 Mn.

page 251 note * Somewhere near this spot, Mr Grieve of Burntisland found a loose piece of hypersthene, showing a cleavage face over an inch in extent.

page 256 note * The late Rev. Mr organ of Stonehaven had so great an admission for these specimens, that he was wont to spend months in wandering over the Kildrummy and Clova Hills in search of them; and so thoroughly had he scoured the district, that the present writer, who has made repeated journeyings with the same object, was never successful in finding either the original locality, or a single specimen.

page 264 note * 8 Fevrier 1875.

page 265 note * The “felspar” of the rock of Corstorphine Hill is usually called albite,—it has not been analysed.

page 265 note † It also constitutes the bulk of the grey granite of Aberdeen; this I find to consist of a great deal of oilgoclase, little orthoclase, little quartz, very small quantities of muscovite, and a good deal of Haughtonite, such a compound as G.Rose calls granitite. The hornblendic gneiss of the Cape Wrath district frequently consists almost solely of a granular mixture of oilgoclase and hornblende.

page 266 note * Except as regards the discrimination of oilgoclase and andesine.