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A butterfly-twin of Gypsum1

Published online by Cambridge University Press:  14 March 2018

L. J. Spencer
L. J. Spencer*
Affiliation:
Mineral Department of the British Museum
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Extract

The specimen here described was acquired in 1913 for the mineral collection of the British Museum. It came from one of the numerous sulphur mines in the province of Girgenti, Sicily. Being of some size (15 cm. = 6 inches across) and with the two individuals well separated and symmetrically disposed, it affords a striking illustration of a twin growth. The crystal is colourless and perfectly transparent; it encloses one or two small patches of native sulphur and compact limestone. A portion, probably about one-third, of the original specimen has been broken away along the perfect cleavage of gypsum ; and this fact, together with the amall point of attachment, increases the resemblance of the twin to tbe butterfly form, which is here more striking than in the so-called butterfly-twins of calcite.

Type
Research Article
Information
Mineralogical magazine and journal of the Mineralogical Society , Volume 18 , Issue 83 , November 1916 , pp. 82 - 86
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1916

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Footnotes

1

Communicated by permission of the Trustees of the British Museum.

References

page 82 note 1 Regd. No. B. M. 1918, 339.

page 83 note 1 Calculated from Des Cloizeaux's angles as quoted by Dana, 'System of Mineralogy,' 6th edition, 1892.

page 84 note 1 Fletcher, M., 'Note on some artificially-produced crystals of Gypsum.' Mineralogical Magazine, 1911, vol. xvi, pp. 187–189 Google Scholar.

page 86 note 1 Hessenberg, F., 'Mineralogische Notizen,' Abhandl. Senckenb. Naturf. Ges, 1872, vol. viii, p. 35, plate 2, figs. 22 and 25Google Scholar.

page 86 note 2 Laeroix, A., 'Le Gypee de Paris...', Nouv. Arch. Museum Hist. Nat. Paris, 1907, ser. 8, vol. ix, p. 914 Google Scholar ; 'Mineralogie de la France,' 1910, vol. iv, p. 182.