Abstract
Ocelli are rounded structures containing polycrystalline feldspar aggregates and minor amounts of mafic minerals; they occur in lamprophyre dykes all over the world. Ocelli are usually interpreted in terms of liquid immiscibility1–3. In alkaline lamprophyre dykes along the south coast of Norway4, ocelli are closely associated with globular structures (varioles) which I have assumed5 were formed as a result of a splitting of the magma into two fractions. The re-examination of these Norwegian dykes reported here, however, has shown that varioles, ocelli and leucocratic feldspar-rich segregations formed by spherulitic and closely related growth mechanisms from under-cooled volatile-rich magmas without an intervening stage of liquid phase separation.
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Carstens, H. Spherulitic crystallization in lamprophyric magmas and the origin of ocelli. Nature 297, 493–494 (1982). https://doi.org/10.1038/297493a0
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DOI: https://doi.org/10.1038/297493a0
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