Hornblende is a complex calcic amphibole series — not a single species but a name historically applied to dark green-black amphiboles in igneous and metamorphic rocks. It is one of the most abundant rock-forming minerals on Earth. Modern IMA classification splits Hornblende into magnesio-hornblende and ferro-hornblende endmembers, but the classical “Hornblende” name remains in widespread use.
Key Facts
- Mohs hardness 5–6.
- Monoclinic amphibole; long prismatic crystals with ~120°/60° cleavage angles.
- Major component of granodiorite, diorite, gneiss, and amphibolite.
- Distinguished from pyroxene by cleavage angles (amphibole ~120°, pyroxene ~87°).
- Common phenocryst in andesite and intermediate volcanic rocks.
Notable Localities
Pargas (Finland) and Bilin (Czech Republic) are classic European sources. Renfrew (Ontario, Canada) supplies massive hornblende.
