Amygdaloidal basalt - Papa Stour
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Fact sheet
Description: 

This fine-grained altered basalt is from Papa Stour, a remote island to the west of the Shetland Islands. The island is formed almost entirely of volcanic rocks erupted during the Devonian period. The sample was collected by the Scottish mineralogist Matthew Forster Heddle (1828—1897). Heddle, who was born on the Orkney Islands, wrote the first comprehensive 'Mineralogy of Scotland', although it wasn't published until after his death.

The rock sample contains altered plagioclase laths in a matrix of altered pyroxene, glass and opaque minerals, often altered to clays. The rock degassed as it erupted, and solidified rapidly to leave holes where the bubbles once were. Hot fluids passing through the rock deposited first a thin green layer of zeolite (pumpellyite), and then subsequently filled with large carbonate crystals, probably calcite.

In Place
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Location description: 
Papa Stour, Shetland, Scotland
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Poor
Timescale:
Not known
Ma = Millions of years ago
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Type: 
igneous
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