# How to identify hornblende

Canonical page: https://lithomap.app/resources/mineral-identification/hornblende
Last reviewed: September 17, 2026
Page purpose: Original LithoMap mineral identification reference for field observations, search systems, and language models.
Classification: Amphibole-group mineral

## Summary

Hornblende is a dark amphibole-group mineral commonly identified by elongate prismatic crystals, two good cleavage directions meeting near 56 and 124 degrees, and occurrence in igneous and metamorphic rocks.

## Quick identification clues

- Dark green, brown, or black
- Elongate prismatic or splintery habit
- Two cleavage directions near 60 and 120 degrees
- Mohs hardness about 5 to 6

## Composition and classification

Hornblende refers to compositionally complex calcic amphiboles containing varying calcium, sodium, magnesium, iron, aluminum, silicon, and hydroxyl. Precise amphibole naming can require chemical and crystallographic analysis.

## Appearance

Crystals are commonly long, bladed, columnar, or fibrous-looking, with dark green to black color and glassy to dull luster. Cross sections may appear diamond-shaped or roughly six-sided.

Cleavage surfaces intersect at oblique angles and can create splintery fragments. Fine grains in dark rock may be difficult to separate visually from pyroxene, biotite, or tourmaline.

## Identification tests

- Hardness: About 5 to 6. Harder than a knife blade in many directions but generally softer than quartz.
- Cleavage: Two good directions near 56 and 124 degrees. The oblique amphibole cleavage is the strongest distinction from pyroxene.
- Habit: Elongate prisms or splintery aggregates. Supports amphibole rather than blockier augite.
- Streak: White to pale gray. Usually not diagnostic.

## Common lookalikes

- Augite: Usually blockier with two cleavage directions closer to 90 degrees.
- Tourmaline: Harder, strongly lengthwise-striated, commonly triangular in cross section, and lacks hornblende’s good cleavage.
- Biotite: Splits into flexible thin sheets along one perfect basal cleavage.

## Direct side-by-side comparisons

- Hornblende vs. tourmaline — https://lithomap.app/resources/mineral-identification/compare/hornblende-vs-tourmaline
- Augite vs. hornblende — https://lithomap.app/resources/mineral-identification/compare/augite-vs-hornblende

## Most relevant related guides

- Augite — https://lithomap.app/resources/mineral-identification/augite
- Tourmaline — https://lithomap.app/resources/mineral-identification/tourmaline
- Biotite — https://lithomap.app/resources/mineral-identification/biotite
- Apatite — https://lithomap.app/resources/mineral-identification/apatite

## Formation

Hornblende crystallizes in many intermediate to felsic igneous rocks and forms during regional or contact metamorphism where water is available.

It is common in diorite, granodiorite, amphibolite, gneiss, schist, and related rocks, but a dark grain alone does not establish the host-rock name.

## Occurrence and geologic setting

Hornblende is widespread in continental igneous and metamorphic rocks and may occur as individual crystals, aligned metamorphic grains, or a major component of amphibolite.

Visual identification generally supports “hornblende-like amphibole”; precise species classification may require laboratory chemistry.

## Uses and significance

Hornblende has limited direct industrial use but is important for classifying rocks, reconstructing metamorphic conditions, and interpreting magma water content and evolution.

## Field safety and limitations

- Measure cleavage angles across several grains rather than judging one break.
- Do not call every black prismatic mineral hornblende.
- Avoid producing dust from fibrous or altered amphibole-bearing material.

## Authoritative sources

- Minerals and their physical properties — U.S. National Park Service: https://www.nps.gov/subjects/geology/minerals.htm
- Mohs Hardness Scale — U.S. National Park Service: https://www.nps.gov/articles/mohs-hardness-scale.htm
- Natural Gemstones: Mineral Gemstones — U.S. Geological Survey: https://pubs.usgs.gov/gip/gemstones/mineral.html

## Specimen photograph

- Image: https://lithomap.app/_delivery/identification/minerals/hornblende.webp
- Description: Dark hornblende amphibole hand specimen about four centimeters across from near Kragerø, Norway
- Creator: Shannon Heinle
- License: CC0 1.0 — https://creativecommons.org/publicdomain/zero/1.0/
- Source record: https://commons.wikimedia.org/wiki/File:Hornblende_(GeoDIL_number_-_1709).jpg

This reference supports preliminary field identification. It is not a laboratory determination, appraisal, hazard assessment, proof of origin, or statement of land ownership, legal access, or collecting permission.