Distribution
They frequently occur in the form of dikes or segregations in gabbro and peridotite: in Shetland, Cortland on the Hudson river, North Carolina (websterite), Baltimore, New Zealand, and in Saxony.
The pyroxenites are often subject serpentinization under low temperature retrograde metanorphism and weathering. The rocks are often completely replaced by serpentines, which sometimes preserve the original structures of the primary minerals, such as the lamination of hypersthene and the rectangular cleavage of augite. Under pressure-metamorphism hornblende is developed and various types of amphibolite and hornblende-schist are produced. Occasionally rocks rich in pyroxene are found as basic facies of nepheline syenite; a good example is provided by the melanite pyroxenites associated with the borolanite variety found in the Loch Borralan igneous complex of Scotland.
Read more about this topic: Pyroxenite
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