CHIASTOLITE SLATE - Lake District
« backCHIASTOLITE SLATE
475 million years old (Ordovician period)
Glenderaterra Valley,
near Skiddaw, Cumbria.
An outcrop of slate in the Glenderaterra Valley in the Lake District displays the rather striking mineral chiastolite which is a variety of andalusite (an aluminium silicate). The name chiastolite comes from the Greek word for cross as it contains carbon inclusions giving it a cross-shaped appearance.
The original sediments were probably mudstones that underwent thermal metamorphism due to the nearby intrusion of molten magma that now forms the Skiddaw granite. The metamorphism converted the rock into a slate and led to the formation of new minerals, one of which was chiastolite.
Chiastolite slate is a classic British rock type well known to students of geology. This example is from an old collection. It was collected in 1968.
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Size: approx. 12 x 8.5 x 2 centimetres
Weight: 270 grams