Letter | Published:

Some New Types of Pleochroic Haloes

Naturevolume 140page191 (1937) | Download Citation

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Abstract

EXAMINATION of a large number of biotite specimens from all parts of the world by my students and myself1 has shown the existence of six distinct types of pleochroic haloes. Two of these, the common type due to uranium and the rarer thorium type, arise from parent radioactive elements of such long periods that α-rays are still being emitted and the darkening of the ring structure is still progressing in these haloes. The remaining four types appear to arise from parents of such short periods that all activity must have long since ceased. The first two types may be referred to as 'active' haloes and the last four as 'extinct' haloes.

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References

  1. 1

    Proc. Roy. Soc., A, 145, 563, 582 (1931); 158, 199 (1937).

  2. 2

    Phil. Trans., 217, 51 (1917).

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Affiliations

  1. Dalhousie University, Halifax, N.S.

    • G. H. HENDERSON

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https://doi.org/10.1038/140191a0

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