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The Cerargyrite Group (holohedral-cubic silver haloids)

  • G. T. Prior (a1) and L. J. Spencer (a1)

Extract

Historical Introduction.—As given in modern text-books, the holohedral-cubic silver haloids occurring as minerals include the following species: the pure chloride, chlorargyrite, AgCl. ; the pure bromide, bromargyrite, AgBr; the intermediate embolite, Ag(Cl,Br), containing chlorine and bromine in varying proportions ; and iodobromite, containing all three halogens in a definite ratio corresponding to the formula 2AgCl.2AgBr.AgI.

The terms hornsilver (used by Gesner as far back as 1565) and cerargyrite (Beudant, 1832) are usually taken as referring only to the pure chloride. As regards their signification, however, they are equally applicable to all of the above species, and in lack of chemical analyses were certainly so applied in the past. Thus Breithaupt, after the discovery of the bromide and chloro-bromide of silver by Berthier in 1841 and 1842, remarks that many of the specimens of ‘Hornerz’ in the Werner Museum having a greenish colour probably contained bromine.

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Page 175 note 1 Zeits. Kryst. Min., 1877, vol. i, pp. 506-7 ; Neues Jahrb. Min., 1878, pp. 619-23 (Abstract in this Magazine, vol. ii, p. 237).

Page 175 note 2 Ueber das Vorkommen der Chlor-, Brom- und Jodverbindungen des Silbers in der Natur (Ein Beitrag zur Kenntniss der geologischen und bergbauliehen Verhältnisse). Marburg, 1870, 47 pp., 4 plates. (Also as Habilit.-Schrift, Marburg, 1869.)

Page 175 note 3 Ann. des Mines, 1853, ser. 5, vol. iv, p. 332.

Page 175 note 4 Traité de Minéralogie, 2nd edition, 1856, vol. iii, pp. 452, 460.

Page 175 note 5 Journ. and Proc. Roy. Soc. N.S.W., 1888, vol. xxii, p. 365

Page 180 note 1 These crystals of silver are rarely suitable for goniometric measurement, but on one of them the forms a {100}, d {110}, and {10.3.0} were determined. The form {10.3.0} does not appear tohave been previously recorded on native silver: measured to a (100), 161/2° to 17° ; calculated (100) : (10.8.0)= 16° 42′ (L. J. S.).

Page 183 note 1 Rodwell, G. F. has determined the specific gravity, melting point and coefficient of expansion of such artificial mixtures (Proc. Roy. Soc., 1876, vol. xxv, p. 292 ; Phil. Trans., 1888 (1882), vol. clxxiii, p. 1189).

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