Notes on mineralogy. No. II. On the chemical composition of the granites of the south-east of Ireland / by Samuel Haughton.

  • Haughton, Samuel.
Date:
[1855]
Catalogue details

Licence: Public Domain Mark

Credit: Notes on mineralogy. No. II. On the chemical composition of the granites of the south-east of Ireland / by Samuel Haughton. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    Then, on the hypothesis that the granite is composed exclu- sively of quartz, felspar, and mica (margarodite), since Quartz = ^\0^ Felspar = R0, SiQs + R^O^ SSiO^ Margarodite =:R0, Si03 + 2(K2 0^ SiO^) 4-2110, we find, if Q, F, M denote the number of atoms of quartz, fel- spar, and margarodite present in the granite, the following rela- tions :— o = Q + 4F + 3M^ A = F + 2M I (1) c = F-fM J In these equations, a, h, c are given by the analysis; and from these equations, Q, F, M ma)- be found. Having deter- mined Q, F, M, we can obtain the per-centages corresponding to them by multiplying Q, F, M by their respective atomic weights. Tiie atomic weight of quartz is known, and is 46; but the atomic weights of felspar and mica vary with the rela- tive proportions of the ingredients composing these minerals. Assuming the average of the analyses of micas from this granite range already given by me (Phil. Mag. vol. ix. p. 272), it is easy to infer from it an atomic weight of mica equal to 305. This atomic weight of mica has been used by me in the calculations made in this paper, and the per-centages of felspar found by difference. The calculations just mentioned do not prove that the gra- nites to which they are applied are composed of quartz, felspar and mica, as combinations of other minerals might equally well represent the analyses; but on the hypothesis that the granites are composed of these three minerals, they give their per-centages with a close degree of apj)roximation : and further, if the equa- tions cannoi be satisfied with positive values of Q, F, M, it may be considered as proved that the granite under consideration cannot be simply a compound of quartz, felspar and marga- rodite. It is to be observed, that if a granite be composed of four or more n)inerals, it is not ])o.-sible to find by the process just de- scribed, the per-centages of each mineral, because in this case the number of unknown quantities is greater than that of the equa- tions from which they are to be calculated. The following Table contains the analyses of eight granites taken from north to south along the principal granite chain, and the notes appended contain a few interesting particulars respect- in a: each granite.