What does amphibolite mean?
Amphibolite is a coarse-grained metamorphic rock made up predominantly of hornblende — a dark, prismatic amphibole mineral — together with plagioclase feldspar. It typically forms when basaltic or gabbroic rocks are subjected to regional metamorphism at moderate to high temperatures and pressures, producing a dense, dark green to black rock that may be massive or distinctly banded. The term belongs firmly to the vocabulary of geologists and earth scientists: it appears in field guides, academic papers, and discussions of metamorphic grade, most famously in the phrase 'amphibolite facies', which denotes a specific set of pressure–temperature conditions under which certain mineral assemblages are stable. Because amphibolites often represent deeply buried fragments of ancient oceanic crust, they play an important role in reconstructing mountain belts and early Earth history. The word derives from the Greek 'amphibolos', meaning ambiguous or doubtful, a reference coined by early mineralogists who struggled to distinguish its constituent minerals.
nounA metamorphic rock composed chiefly of the minerals hornblende (an amphibole) and plagioclase feldspar, typically dark green to black in colour and formed under medium-to-high temperature and pressure conditions.
- A coarse-grained metamorphic rock consisting mainly of hornblende and plagioclase, formed by regional metamorphism of basaltic or gabbroic rocks.
"The ancient basement of the mountain range consists largely of banded amphibolite and gneiss."
"The road cut exposed a dark band of amphibolite squeezed between layers of pale quartzite."
"Geologists dated the amphibolite facies assemblages to reconstruct the region's ancient burial depths."
Plural form is standard when referring to multiple occurrences, bodies, or samples of the rock.
"Archaean terranes commonly contain several distinct amphibolites of different ages."
The word comes from the Greek 'amphibolos', meaning 'ambiguous' — fitting for a rock whose very name was coined because its minerals were so hard to tell apart.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of amphibolite
Amphibolite takes its name from the Greek 'amphibolos', meaning 'ambiguous' or 'doubtful'. The French mineralogist René Just Haü applied this root when naming the amphibole group around the turn of the nineteenth century, reflecting the difficulty of distinguishing these similar-looking minerals; the rock name followed from the dominant mineral. The Greek prefix 'amphi-' means 'on both sides' or 'around', and it also survives in English words such as 'amphibious' and 'amphibian'. The term entered geological usage in the nineteenth century as metamorphic petrology developed as a discipline.
Related word forms
How amphibolite is actually used
Strictly a technical term of petrology and geology; it appears almost exclusively in scientific, academic, and field-guide contexts rather than everyday speech.
Easily confused with amphibolite
Amphibole is a group of silicate minerals (such as hornblende), whereas amphibolite is a whole rock composed largely of those minerals.
Greenschist is a lower-grade metamorphic rock containing chlorite and epidote, while amphibolite forms at higher metamorphic grades dominated by hornblende.