Identification guide · Minerals
How to Identify Hornblende
Hornblende forms elongated, six-sided prismatic crystals, typically black, dark green, or brown, with a vitreous to dull luster and a pale gray to greenish streak. Hardness ranges from 5 to 6, and its two cleavage planes intersect at approximately 56 and 124 degrees, the classic amphibole angle used to separate it from pyroxenes like augite, whose cleavage meets closer to 90 degrees. Crystal habit is long and prismatic rather than the stubby form typical of pyroxene. It is most reliably distinguished from augite by carefully measuring this cleavage angle under magnification.
Hornblende identification checklist
| Color | Black, Dark green, Dark brown | Look at a clean, dry surface in daylight. Color zoning, banding or spots are as diagnostic as the hue. |
|---|---|---|
| Luster | Vitreous to silky | Fresh surfaces shine like glass; a dull surface usually means weathering, so chip or wet a corner. |
| Transparency | Translucent to opaque | Hold a thin edge up to a bright light and note whether light passes through. |
| Mohs hardness | 5–6 | It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will. |
| Streak | Pale gray to colorless | Drag a corner across unglazed porcelain (the back of a bathroom tile) and check the powder color. |
| Cleavage | Perfect prismatic, two directions (~56°/124°) | |
| Fracture | Uneven | |
| Specific gravity | 3.0–3.4 | Heavier than it looks (specific gravity about 3.2). |
| Crystal system | Monoclinic |
Hornblende look-alikes and how to tell them apart
Both sit near Mohs 5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Hornblende vs Actinolite →
Both sit near Mohs 5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Hornblende vs Aegirine →
Both sit near Mohs 5–6, so a scratch test alone will not separate them. Lean on luster, streak and heft instead. Hornblende vs Augite →
Andradite is harder (Mohs 6.5–7) than Hornblende (Mohs 5–6), so Andradite will scratch Hornblende and not the other way round. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will.
Hornblende identification FAQ
How can you tell if a rock is Hornblende?
Check the color (black, dark green, and dark brown), the vitreous to silky luster, a Mohs hardness of 5–6 and a pale gray to colorless streak. Photographing it with the StoneSnap app gives a match in seconds.
What is the hardness of Hornblende?
Hornblende has a Mohs hardness of 5–6. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will.
What is the difference between Hornblende and Actinolite?
Hornblende (Mohs 5–6, vitreous to silky luster) and Actinolite (Mohs 5–6, vitreous to silky luster) look alike, but hardness, streak and heft usually separate them. See the full Hornblende vs Actinolite comparison for a side-by-side table.
Is Hornblende worth anything?
Entry-level Hornblende specimens sell for around $2, typical collector pieces about $20, and premium examples $150 or more depending on size, quality and locality.
What color is Hornblende?
Hornblende is most often black, dark green, and dark brown. Color varies with impurities and locality, so confirm with hardness and luster rather than color alone.
