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Note on a Picrite from the Liskeard District
Published online by Cambridge University Press: 14 March 2018
Extract
Specimens of this rock were presented a short time since to the British Museum by the Earl of St. Germans, and Mr. T. Davies, knowing my interest in pierites and peridotites, kindly requested me to examine them and communicate the results to the Mineralogical Society. The rock occurs, as I am informed, in boulders between Menheniot and St. Germans. The picrite of the Clicker Tor, near the former place, is well known and has been more than once described, but, as all specimens which I have seen from that locality are very different, macroscopically and microscopically, from those now sent to me, it may be well to put on record a description of the latter, which, after the excellent summary of the mineral character of picrites given in Mr. Teall's British Petrography, need not be lengthy.
- Type
- Research Article
- Information
- Mineralogical magazine and journal of the Mineralogical Society , Volume 8 , Issue 37 , October 1888 , pp. 108 - 111
- Copyright
- Copyright © The Mineralogical Society of Great Britain and Ireland 1888
References
page 108 note 1 Quart. Journ. Geol. Soc. Vol. XLI. p. 511.
page 108 note 2 Determined for me, by Prof. Ramsay's kindness, in the Laboratory (Chemical) of University College.
page 109 note 1 For description see Teall, pp. 90-95.
page 109 note 2 Ibid. pp. 90-94.
page 110 note 1 It is a curious fact, to which I have already called attention (Geol. Mag. Dec.iii. Vol. IV. p. 380), that the percentage of alumina in piorites is often higher than we should expect; microscopic examination indicating that felspar is very rare, and neither suggesting its former presence nor disclosing minerals in any quantity that are likely to be rich in alumina.
page 110 note 2 Quart. Jour. Geol. Soc. Vol. XLI. p. 519.
page 110 note 3 Quart. Jour. Geol. Soc. Vol. XLI. p. 120.
page 111 note 1 Quart. Jour. Geol. Soc. Vol. XLI. p. 520.
page 111 note 2 British Petrography, p. 95. It is quite true that some uralite shows a fibrous structure, and this may be so with Rose's original type; but as the structure has been disclosed by the microscope and was not dominant in the original definition, I see no advantage in restricting the term.
page 111 note 3 Can it be a slight hydration, for glauoonite, ohlorites and alteration products after sundry ferro-magnesian silicates are green ?