Hornblende Gneiss
“Banded beauty from the deep crust”
Hornblende gneiss is a high-grade metamorphic rock featuring alternating dark bands rich in hornblende and light bands of quartz and feldspar. It forms from the intense metamorphism of mafic igneous or sedimentary rocks and makes up significant portions of ancient continental shield regions.
hornblende, plagioclase feldspar, quartz, biotite, garnet (occasional)
Canadian Shield, Lewisian Complex (Scotland), Lofoten (Norway), Dharwar Craton (India), Adirondacks (USA)
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The Lewisian gneiss of northwest Scotland is roughly 3 billion years old — among the oldest rocks in Europe, formed before any complex life existed on Earth.
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What does the mineral assemblage of hornblende gneiss reveal about its protolith (parent rock)?
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