Augite is one of the most common minerals in the pyroxene group and an important rock-forming mineral in igneous and metamorphic rocks. It is typically dark green, dark brown, or black and is especially abundant in basalt, gabbro, and other mafic rocks.
Because augite forms at relatively high temperatures, it provides valuable information about magma composition and crystallization processes.
Augite is important because it:
- forms in many volcanic and plutonic rocks
- helps geologists interpret magma evolution
- is a major ferromagnesian mineral
- demonstrates pyroxene crystal structures
Learn more → what is a mineral
What Is Augite?
Augite is a calcium-magnesium-iron pyroxene mineral. Its composition varies, but a generalized formula is:
Augite contains varying amounts of:
- calcium
- magnesium
- iron
- aluminum
- silicon
It belongs to the pyroxene mineral group.
Basic Properties of Augite
| Property | Value |
|---|---|
| Mineral Group | Pyroxene |
| Chemical Class | Silicate |
| Crystal System | Monoclinic |
| Hardness | 5.5–6 |
| Streak | White to Gray |
| Luster | Vitreous |
Why Is Augite Dark?
Augite's color is caused by Iron and Magnesium Content
These elements give augite:
- dark green coloration
- dark brown coloration
- black appearance
Like hornblende and biotite, augite is considered a ferromagnesian mineral because it is rich in iron and magnesium.
Crystal Structure of Augite
Augite belongs to the pyroxene group and contains single-chain silicate structure
Its crystal structure consists of linked silicate tetrahedra arranged in single chains.
This structure produces:
- blocky crystal habits
- characteristic cleavage
- relatively high density
Learn more → crystal-structure-in-minerals
Crystal System of Augite
Augite belongs to the monoclinic crystal system. Its crystallographic relationship is:
Augite typically forms:
- short prismatic crystals
- blocky crystals
- granular masses
Learn more → monoclinic-crystal-system
Physical Properties of Augite
| Property | Description |
|---|---|
| Color | Dark green, brown, black |
| Streak | White to gray |
| Luster | Vitreous |
| Hardness | 5.5–6 |
| Cleavage | Two directions |
| Fracture | Uneven |
| Specific Gravity | 3.2–3.6 |
Augite Cleavage
One of augite's most important identification features is cleavage near 90°. Augite displays two cleavage directions intersecting at approximately: . This feature helps distinguish augite from amphiboles such as hornblende.
Learn more → mineral-cleavage-vs-fracture
How Augite Forms
Augite commonly forms through:
Magmatic Crystallization
Crystallizes directly from magma.
Volcanic Processes
Abundant in basaltic lava flows.
Plutonic Processes
Forms in slowly cooled intrusive rocks.
Metamorphism
Occurs in some high-temperature metamorphic rocks.
Augite in Igneous Rocks
Augite is commonly found in:
Basalt
One of the most abundant minerals.
Gabbro
Major constituent of coarse-grained mafic rocks.
Andesite
Common in intermediate volcanic rocks.
Diabase
Frequently contains abundant augite.
Common Augite-Bearing Rocks
| Rock Type | Occurrence |
|---|---|
| Basalt | Very Common |
| Gabbro | Very Common |
| Andesite | Common |
| Diabase | Common |
Augite vs Hornblende
| Property | Augite | Hornblende |
|---|---|---|
| Structure | Single Chain | Double Chain |
| Crystal Habit | Blocky | Elongated |
| Cleavage Angles | ~90° | 56° & 124° |
| Water Content | Low | Higher |
The cleavage angle is usually the easiest way to tell them apart.
Learn more → hornblende-mineral-explained
Geological Importance of Augite
Augite helps geologists understand:
- magma chemistry
- crystallization temperatures
- volcanic processes
- mantle-derived magmas
Its presence often indicates formation under relatively high temperatures.
Industrial and Scientific Uses
Although augite has limited direct commercial use, it is important in:
Geological Research
Studying magma evolution.
Mineral Collections
Common educational mineral.
Petrology
Understanding igneous rocks.
Scientific Analysis
Investigating volcanic processes.
Major Uses of Augite
| Field | Application |
|---|---|
| Geology | Rock studies |
| Education | Mineral collections |
| Research | Petrology |
| Volcanology | Magma analysis |
Augite in Mineral Identification
Geologists identify augite using:
- dark green to black color
- blocky crystal habit
- cleavage near 90°
- hardness of 5.5–6
- vitreous luster
The nearly right-angle cleavage is one of the most reliable diagnostic features.
Learn more → mineral-identification-guide
Augite Identification Summary
| Property | Augite |
|---|---|
| Hardness | 5.5–6 |
| Crystal System | Monoclinic |
| Cleavage | 87° & 93° |
| Color | Dark Green–Black |
| Structure | Single-Chain Silicate |
| Mineral Group | Pyroxene |
Augite is a common dark-colored pyroxene mineral found in many igneous and metamorphic rocks.
Augite is typically dark green, dark brown, or black.
Its blocky crystals and cleavage angles near 90° are key identification features.
Augite belongs to the monoclinic crystal system.
Augite is abundant in basalt, gabbro, and other mafic igneous rocks.
Final Thoughts
Augite is one of the most important pyroxene minerals and a major component of many igneous rocks. Its single-chain silicate structure, characteristic cleavage, and widespread occurrence make it a key mineral for understanding magma evolution and volcanic processes.
From basaltic lava flows to deep intrusive rocks, augite provides valuable clues about the formation and evolution of Earth's crust and mantle.
