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34
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THE MATRIX OF THE DIAMOND
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It
is very common to find the small perovskite crystals surrounding a
large crystal of olivine, as if attracted to it. The following figures
are examples of this peculiarity :—
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The
perovskite crystals lie on the outer sides of the olivine crystal, as
if a later growth. In the same manner perovskite is attached to the
outer surface of serpentine pseudomorphs after olivine. Fig. 29 shows
such a case, and shows also in the serpentinised olivine secondary
rutile needles growing out of a grain of titanic iron, as already
described under olivine.
A similar grouping of small perovskite crystals, like a wreath, around the olivines has been noticed by Stelzner1 in the melilite-basalt of Hammerer Spitzberg, near Warten-berg, Bohemia (the so-called 'nephelin-pikrit' of Boficky),2 which is rich in perovskite.
Perovskite
is one of the most characteristic minerals for the felspar-free basic
eruptive rocks. As a rock ingredient it was first detected by Boricky3 in the above-named melilite-basalt of Wartenberg. Hussak4 proved its existence in the nepheline and leucite lavas of the Eifel; Stelzner5 showed that it was a constant constituent of melilite-basalts, and Sauer6 that it occurred very commonly in the nepheline and leucite-basalts of the Erzgebirge.
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