File:Garnet lherzolite - xenolith from a kimberlite pipe (Precambrian, likely Archean; Kimberley, central South Africa) 1 (15001208861).jpg

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Garnet lherzolite xenolith nodule (unpolished slice, 9.4 cm across). Dark green crystals = olivine & orthopyroxene Purplish-red crystals = pyrope garnet Bright emerald green crystals = chromian diopside pyroxene.


One of the most incredibly rare rocks in my collection is this garnet lherzolite from South Africa. This is a slice of a xenolith nodule (“xeno” = foreign, and “lith” = rock) from a kimberlite pipe in Kimberley, central South Africa. As magma rises in a pipe during kimberlite formation, it plucks rock from the deep walls of the pipe. Many kimberlite xenoliths turn out to be samples from the deep crust, lithospheric mantle, and even possibly sub-lithospheric mantle. This garnet lherzolite xenolith is such a sample of lithospheric or sub-lithospheric mantle! Rocks such as garnet lherzolite and spinel lherzolite have traditionally been inferred to be primitive mantle materials.

This rock is a variety of peridotite, an ultramafic intrusive igneous rock. It is dominated by two dark-greenish minerals: forsterite olivine (having veinlets of serpentine) and enstatite orthopyroxene. Notice that the rock also contains rounded, purplish-red crystals. These are pyrope garnets. There are also widely scattered, bright emerald green colored crystals of chromian diopside pyroxene. Small amounts of accessory minerals are also present.

Age: Precambrian, very likely Archean (probably late Mesoarchean or early Neoarchean).
Date
Source Garnet lherzolite - xenolith from a kimberlite pipe (Precambrian, likely Archean; Kimberley, central South Africa) 1
Author James St. John

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This file is licensed under the Creative Commons Attribution 2.0 Generic license.
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/15001208861 (archive). It was reviewed on 9 October 2019 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0.

9 October 2019

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Date/TimeThumbnailDimensionsUserComment
current06:16, 9 October 2019Thumbnail for version as of 06:16, 9 October 20191,525 × 1,570 (1.69 MB)Ser Amantio di Nicolao (talk | contribs)Transferred from Flickr via #flickr2commons

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