The Elements of economic geology

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Monograph

Identifikator:: 1773832379

URN:: urn:nbn:de:zbw-retromon-172798

Document type:: Monograph

Author:: Gregory, John W. http://d-nb.info/gnd/11683014X

Title:: The Elements of economic geology

Place of publication:: London

Publisher:: Methuen

Year of publication:: 1928

Scope:: XIV, 312 S.; graph. Darst.

Digitisation:: 2021

Collection:: Economics Books

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Chapter

Document type:: Monograph

Structure type:: Chapter

Title:: Part III. Earthy minerals

Collection:: Economics Books

164 ECONOMIC GEOLOGY diamonds are based on the belief that microscopic diamonds have been made artificially by the reduction of carbon at high temperatures and under great pressure in the presence of metallic iron, lithium, or basic silicates, or by the explosion of cordite in a bomb. These experiments led to the general conclusion that most diamonds were formed during the cooling of ultra-basic igneous rock and native iron. The artificial production of the diamond is however discredited by the work of Sir Charles Parsons in continuation of the researches described in his Bakerian Lecture (Phil. Tr. A., vol. 220, 1926, pp. 67-107). He has examined the specimens ex- hibited to the British Association by Sir William Crookes, and analysed numerous specimens that he has himself made by the methods of Moissan and Crookes; he tells me that the crystals claimed as artificial diamonds are mostly silicon carbides, and other complex carbides of the impurities in the iron, viz. calcium, magnesium, chromium, etc., and that in his opinion no artificial diamond has yet been made.l He adds that for many years he believed the crystals, some of which he exhibited at the Royal Society in 1915, were diamonds, and that they burnt in oxygen at goo® C. ; but on repeating this test with rigorous care the most character- istic crystals were found uncorroded; some few had been whitened but retained their original form. Many facts, such as the nature of kimberlite, the matrix of the diamonds in the chief South African mines, and the presence in diamonds of hydrocarbons and apophyllite which would be decomposed at a high temperature (eg. J. C. Branner, Amer. Journ. Sci., (4), xxxiii, 1912, pp. 25-6, and G. F. Williams, T7. Amer. I.M E., xxxv, 1905, p. 451), indicate that the diamond was not formed at a high temperature. Its geological occurrence is in favour of its formation by the slow crystallization of carbon set free by the dissociation, prob- ably of a hydrocarbon or carbon tetrachloride at a moderate temperature, in material rendered viscous by superheated steam, as at the root of a mud volcano, or where a pheuma- tolytic solution is acting at an igneous contact or is pro- ducing pegmatite. tH. Le Chatelier remarks (Science et Industrie, 1923, P. 194), “ No one believes any more in the diamond of Moissan ”’

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