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IV.—Allotropic Forms of Silica and their Significance as Constituents of Igneous Rocks

Published online by Cambridge University Press:  01 May 2009

Cosmo Johns
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Extract

That silica appears as a constituent mineral of igneous rocks in two distinct phases, viz. quartz and tridymite, has been known for some time. The writer is not aware that any explanation has been offered which would indicate the conditions determining the appearance of one or the other in a cooling fused rock-mass. He now proposes to describe certain experiments made with a view to explain why it is that though the free silica generally appears as quartz, yet occasionally, as in certain trachytes, it crystallizes out as tridymite.

Type
Original Articles
Information
Geological Magazine , Volume 3 , Issue 3 , March 1906 , pp. 118 - 120
Copyright
Copyright © Cambridge University Press 1906

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References

1 Rep. Brit. Assoc., 1900, p. 730.Google Scholar

2 Journ. I. and S. Inst., vol. i (1905), p. 350.Google Scholar