Troctolite
“Spotted like a trout”
Troctolite is a mafic intrusive rock made of olivine and plagioclase feldspar, with dark olivine spots scattered through a lighter feldspar matrix. Its speckled appearance reminded early geologists of trout skin, giving this rock its delightful name from the German word for trout.
plagioclase feldspar, olivine, chromite (accessory), pyroxene (minor), magnetite
Rum (Scotland), Duluth Complex (Minnesota, USA), Bushveld Complex (South Africa), Stillwater Complex (Montana, USA)
6-6.5
On the Isle of Rum in Scotland, layers of troctolite alternate with other rock types in rhythmic bands that formed as minerals crystallized and settled in a magma chamber like snow falling in a lava lake.
Test Your Knowledge
Why is troctolite's name derived from the German word for trout?
Photo Attribution
Title: Coverack Beach - Troctolite - geograph.org.uk - 3132605.jpg
Author: Ashley Dace
License: CC BY-SA 2.0
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