Where is Hornblende found?
Hornblende
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Open the appHornblende occurs in specific geological environments. Knowing where to look, and in what kind of rock, is the difference between going home empty-handed and finding a great specimen.
Where to find Hornblende
Worldwide
Hornblende is a ubiquitous rock-forming mineral and can be found in igneous and metamorphic terrains globally. Notable occurrences include the Adirondack Mountains (USA), various localities in Canada, Scandinavia, and many mountain ranges where regional metamorphism has occurred.
Igneous Intrusions
Common in plutonic rocks like diorite, granodiorite, and syenite, often forming large, well-formed crystals.
Volcanic Rocks
Present in volcanic rocks such as andesite and dacite, typically as phenocrysts.
Metamorphic Terrains
Abundant in amphibolites, hornblende schists, and gneisses, which are products of medium- to high-grade metamorphism of mafic igneous rocks or certain sedimentary protoliths.
Collecting tips
- Look for Dark, Prismatic Crystals. Hornblende typically appears as dark (green, brown, black) elongated crystals within lighter-colored matrix minerals like feldspar or quartz.
- Check for Characteristic Cleavage. The most definitive field test is to observe the two cleavage planes intersecting at oblique angles (56° and 124°). This distinguishes it from pyroxenes (like augite) which have cleavage at nearly 90°.
- Examine Rock Type. Hornblende is a primary constituent of amphibolite. If you find a dark, medium- to coarse-grained metamorphic rock composed mainly of amphibole, it's likely hornblende.
- Consider Associated Minerals. In igneous rocks, it's often found with plagioclase feldspar, quartz, and biotite. In metamorphic rocks, it can be associated with garnet, epidote, and plagioclase.
Quick Check
- Color:
- Dark green to black
- Luster:
- Vitreous to sub-vitreous
- Streak:
- White to grayish-green
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