Hostname: page-component-cd9895bd7-lnqnp Total loading time: 0 Render date: 2024-12-26T18:18:22.406Z Has data issue: false hasContentIssue false
  • English
  • Français

Stratiform magnetite crystals of abnormal morphology from volcanic carbonatites in Tanzania, Kenya, Greenland, and India

Published online by Cambridge University Press:  05 July 2018

T. Deans  and
A. F. Seager
T. Deans
Affiliation:
20 Grove Park Road, Chiswick, London W4 3SD
A. F. Seager
Affiliation:
Department of Geology, Birkbeck College, University of London, 7/15 Gresse Street, London WIP IPA
Get access Rights & Permissions [Opens in a new window]

Summary

Magnetite is common in carbonatites, and usually has octahedral habit. Abnormal crystals from Galapo, Tanzania, were long thought to be unique, but such crystals are now known to occur at seven localities in four countries. The magnetite is titaniferous, but not unusual in composition for its provenance. The abnormal crystals typically have large growth pyramids extending in one direction (occasionally in two or more directions). They appear to be formed by superimposition of macroscopic growth sheets, parallel to octahedral and other planes, giving a planar structure to the growth pyramid. The edges of the sheets may form low-index or more complex surfaces. Some sheets project beyond the bounding planes of the growth pyramid, which is not repeated in crystallographically equivalent orientations. This unusual mode of growth will be called stratiform. Recognition of these distinctive crystals elsewhere might reveal the presence of hitherto unsuspected carbonatites.

Type
Research Article
Information
Mineralogical Magazine , Volume 42 , Issue 324 , December 1978 , pp. 463 - 475
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1978

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Bishop, (W. W.), 1968. Trans. Leicester Lit. Phil. Soc. 72, 22–44.Google Scholar
Bishop, (W. W.), Miller, (J. A.), and Fitch, (F. J.), 1969. Am. J. Sci. 267, 669-99 [M.A. 23-250].CrossRefGoogle Scholar
Deans, (T.), Sukheswala, (R. N.), Sethna, (S. F.), and Viladkar, (S. G.), 1972. Trans. Instn. Min. Metall. 81, sect. B, I 10 [M.A. 23-333].Google Scholar
King, (B. C.), Le Bas, (M. J.), and Sutherland, (D. S.), 1972. J. geol. Soc. 128, 173–205 [M.A. 23-326].CrossRefGoogle Scholar
Le Bas, (M. J.), 1977. Carbonatite-nephelinite volcanism (London etc., John Wiley & Sons).Google Scholar
Le Bas, (M. J.) and Dixon, (J. A.), 1965. Nature, 207, 68.CrossRefGoogle Scholar
McCall, (G. J. H.), 1958. Rep. Geol. Surv. Kenya, 45, [M.A. 14-357].Google Scholar
Patel, (A. R.) and Tolansky, (S.), 1957. Proc. R. Soc. A, 243, 41 [M.A. 14 121].Google Scholar
Prins, (P.), 1972. Lithos, 5, 227-40 [M.A. 24-69].CrossRefGoogle Scholar
Shackleton, (R. M.), 1951. Q. J. geol. Soc. Lond. 106, 345-92.CrossRefGoogle Scholar
Stewart, (J. W.), 1970. Med. om Grønland, 186, nr. 4.Google Scholar
Sukheswala, (R. N.) and Borges, (S. M.), 1975. Indian J. Earth Sci. 2, no. 1, 1–10 [M.A. 27-104].Google Scholar
Tuttle, (O. F.) and Gittins, (J.), 1966. Carbonatites (London, Wiley & Sons) [M.A. 18-210].Google Scholar
Van Couvering, (J. A.) and Miller, (J. A.), 1969. Nature, 221, 628-32 [M.A. 21-189].CrossRefGoogle Scholar
Whitworth, (T.), 1953. Q. J. geol. Soc. Lond. 109, 75–96.CrossRefGoogle Scholar