Appinite
“Dark, coarse hornblende from the magma mixing zone”
Appinite is a dark, coarse-grained plutonic rock dominated by hornblende, often with plagioclase and biotite. These rocks form when hot, water-rich mafic magma is injected into a granitic magma chamber, producing vigorous hornblende crystallization at the mixing interface.
hornblende (dominant), plagioclase, biotite, quartz (minor), alkali feldspar, apatite, titanite
Appin (Scottish Highlands — type locality), Donegal (Ireland), Iberian Peninsula, Maine (USA), Newfoundland (Canada)
5-6.5
Appinite suites in the Scottish Highlands are interpreted as 'plumbing systems' that fed water-rich mafic magma into granitic bodies — they reveal the hidden infrastructure beneath ancient volcanic arcs.
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Why does hornblende crystallize so abundantly in appinites compared to other mafic plutonic rocks?
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