Dear Haijin, visitors and travelers,
Our prompt for today, Xenolith, will not be an easy one. I had to search on the Internet to find something about this prompt. And I found the following about Xenolith at Wikipedia.
A xenolith (Ancient Greek: “foreign rock”) is a rock fragment which becomes enveloped in a larger rock during the latter's development and hardening. In geology, the term xenolith is almost exclusively used to describe inclusions in igneous rock during magma emplacement and eruption. Xenoliths may be engulfed along the margins of a magma chamber, torn loose from the walls of an erupting lava conduit or explosive diatreme or picked up along the base of a flowing lava on Earth's surface. A xenocryst is an individual foreign crystal included within an igneous body. Examples of xenocrysts are quartz crystals in a silica-deficient lava and diamonds within kimberlite diatremes.
Although
the term xenolith is most commonly associated with igneous inclusions, a broad
definition could include rock fragments which have become encased in
sedimentary rock. Xenoliths are sometimes found in recovered meteorites.
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| Credits: Xenolith |
To be
considered a true xenolith, the included rock must be identifiably different
from the rock in which it is enveloped; an included rock of similar type is
called an autolith or a cognate inclusion.
Xenoliths and xenocrysts provide important
information about the composition of the otherwise inaccessible mantle.
Basalts, kimberlites, lamproites and lamprophyres, which have their source in
the upper mantle, often contain fragments and crystals assumed to be a part of
the originating mantle mineralogy. Xenoliths of dunite, peridotite and spinel lherzolite
in basaltic lava flows are one example. Kimberlites contain, in addition to
diamond xenocrysts, fragments of lherzolites of varying composition. The
aluminium-bearing minerals of these fragments provide clues to the depth of
origin. Calcic plagioclase is stable to 25 km depth. Between 25 km and about 60
km, spinel is the stable aluminium phase. At depths greater than about 60 km,
dense garnet becomes the aluminium-bearing mineral. Some kimberlites contain
xenoliths of eclogite, which is considered to be the high-pressure metamorphic
product of oceanic basaltic crust, as it descends into the mantle along
subduction zones (Blatt, 1996).I hope you can write/compose a haiku with this prompt ... I couldn't ....
This episode is open for your submissions today at noon (CET) and will remain open until next Friday
October 10th at noon (CET). Have fun ... be inspired and share ... Our next week's prompt will be "Youngsters".
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