Augite is a primary rock-forming mineral found in a wide variety of mafic and intermediate igneous rocks. It typically appears as dull, dark, stubby prismatic crystals that often exhibit a characteristic blocky fracture. Collectors look for its distinctive near-90-degree cleavage angles, which help distinguish it from the more elongated, splintery appearance of hornblende.
Is this augite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch augite with a known reference. Augite sits at Mohs 5.5-6, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Streak: gray-green.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous, resinous to dull.
- 4Match the color rangeCompare against the expected color range: black, dark green, brownish green, brown green, green, light brown, dark brown.
- 5Look at form & habitCrystal system: monoclinic. Typical habit: columnar, granular, massive.
Often confused with
Augite vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Streak differs, so Augite leaves gray-green, Hornblende leaves grayish-white.
How to tell apart: Streak differs, so Augite leaves gray-green, Aegirine leaves pale yellowish gray.
How to tell apart: Streak differs, so Augite leaves gray-green, Diopside leaves white, gray, gray-green.
Often found alongside augite
Minerals reported to co-occur with augite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- (Ca,Mg,Fe)₂Si₂O₆
- Mohs hardness
- 5.5-6
- Density
- 3.19-3.56 g/cm³
- Streak
- Gray-green
- Luster
- Vitreous, resinous to dull
- Transparency
- Transparent to opaque
- Crystal system
- Monoclinic
- Crystal habit
- Columnar, granular, massive
- Cleavage
- Good on {110}, (110) ^ (110) ~87°; partings on {100} and {010}
- Rarity
- Common
- Uses
- Collector, Petrological studies
- Host rock
- Essential in mafic igneous rocks, basalt, gabbro; common in ultramafic rocks; in some high-grade metamorphic rocks and metamorphosed iron formations
Where rockhounds find augite
9 mapped spotsClassic worldwide localities
- Franklin and Sterling Hill, Ogdensburg, Sussex Co., New Jersey, USA
- Diana, Lewis Co., and Fine, St. Lawrence Co., New York, USA
- Arendal, Norway
- Vesuvius, Campania, Italy
- Frascati, Alban Hills, Lazio, Italy
- Mt. Monzoni, Val di Fassa, Trentino-Alto Adige, Italy
Field-hunting tip
Where it forms: Essential in mafic igneous rocks, basalt, gabbro; common in ultramafic rocks; in some high-grade metamorphic rocks and metamorphosed iron formations. If you start seeing orthoclase, sanidine, labradorite in float, you are in the right ground. Typical habit: columnar, granular, massive. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Utah, New Jersey, New Mexico. Start trip planning there.
Common questions
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Find augite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
