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On larnite (calcium orthosilicate, a new mineral) and its associated minerals from the limestone contact-zone of Scawt Hill, Co. Antrim

  • C. E. Tilley (a1)

Extract

The contact-zone of Chalk and Tertiary dolerite at Scawt Hill, near Larne, Co. Antrim, consists of an assemblage of comparatively rare minerals, including a mineral of the composition Ca2SiO4 not previously recognized as a naturally occurring compound. In the assemblages of the contact-zone the chief minerals, apart from calcite, are spurrite, calcium orthosilieate (larnite), melilite (gehlenite), merwinite, spinel, perovskite, and wollastonite. Outside this contact-zone, the chalk consists almost wholly of calcium carbonate ; nearer the contact it is recrystallized to a granular mosaic of calcite of coarse texture, while at the immediate contact the chalk is completely transformed into an aggregate of new-formed silicates in varying proportions. A hybrid zone between the dolerite and the exogenous contact-rock is composed Of a coarsely crystalline rock built up essentially of titanaugite, melilite (humboldtilite), nepheline, wollastonite, perovskite, and various zeolites. An account of the melilite of this hybrid zone has already been given.

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page 77 note 1 Tilley, C. E., Geol. Mag., 1929, vol. 66.

page 78 note 1 Tilley, C. E., Min. Mag., 1928, vol. 21, p. xlviii, 1929, vol. 22, p. xxviii; and Geol. Mag., 1927, vol. 64, p. 285.

page 78 note 2 Gough, G. C., Geol. Mag., 1907, dec. 5, vol. 4, p. 145.

page 78 note 3 Wright, F. E., Amer. Journ. Sei., 1908, ser. 4, vol. 26, p. 547.

page 79 note 1 Tilley, C. E., Geol. Mag., 1928, vol. 65, p. 372 . [Min. Abstr., vol. 4, p. 84.]

page 79 note 2 Foshag, W. F., Amer. Min., 1920, vol. 5, p. 80 ; E. S. Larsen and W. F. Foshag, ibid., 1921, vol. 6, p. 143.

page 79 note 3 The Tasmanian mineral recorded as calcium orthosilicate by F. P. Paul (Tschermaks Min. Petr. Mitt., 1906, vol. 25, p. 309), and named shannonite (C. E. Tilley, Geol. Mag., 1927, vol. 64, p. 144) on the basis of Paul’s data, has since been shown to be monticellite (C. E. Tilley, Geol. Mag., 1928, vol. 65, p. 29). Rather than transfer the name ‘shannonite’ to the mineral now described, any further confusion will be avoided by adopting a new name. [See Min. Mag., 1928, vol. 21, p. 576.]

page 81 note 1 Day, A. L, Shepherd, E. S., and Wright, F. E., Amer. Journ. Sci., 1906, ser. 4, vol. 22, p. 294.

page 81 note 2 Rankin, G. A. and Wright, F. E., Amer. Journ. Sci., 1915, ser. 4, vol. 39, p. 7.

page 84 note 1 Larsen, E. S. and Foshag, W. F., Amer. Min., 1921, vol. 6, p. 143.

page 85 note 1 Wright, F. E., Amer. Journ. Sci., 1908, ser. 4, vol. 26, p. 551.

page 85 note 2 Eitel, W., Neues Jahrb. Min., 1923, vol. 48, p. 63.

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Mineralogical Magazine
  • ISSN: 1876-1968
  • EISSN: 2515-821X
  • URL: /core/journals/mineralogical-magazine
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