Chlorite
Chlorite is not a single mineral but a large group of iron- and magnesium-rich phyllosilicates, including clinochlore and chamosite, sharing a layered sheet-silicate structure related to mica. Its name refers to its typical dull to bright green color, caused by iron and magnesium within the crystal lattice. It is one of the most common minerals in low-grade metamorphic rocks.
Chlorite properties at a glance
| Type | Minerals |
|---|---|
| Chemical formula | (Mg,Fe,Al)6(Si,Al)4O10(OH)8 |
| Mohs hardness | 2–2.5 |
| Crystal system | Monoclinic |
| Luster | Vitreous to pearly |
| Streak | Pale green to white |
| Cleavage | Perfect basal, one direction |
| Fracture | Uneven across cleavage; flexible non-elastic flakes |
| Specific gravity | 2.6–3.3 |
| Transparency | Translucent |
| Common colors | Green, Dark green, Blackish green |
| Rarity | common |
Geology & background
Chlorite forms mainly through the retrograde or low-temperature metamorphism of iron- and magnesium-bearing minerals such as biotite, pyroxene, amphibole, and garnet, and it is the defining mineral of the greenschist metamorphic facies. It gives chlorite schist and greenstone their characteristic green color and is also common as an alteration product in weathered basalt, gabbro, and hydrothermally altered granite. Chlorite frequently coats joint surfaces and fills veins in metamorphic terrains worldwide, from the Alps to the Appalachians. For collectors, chlorite is easy to identify but rarely showy, usually appearing as soft, greasy-feeling green flakes or coatings rather than sharp crystals. Its flakes bend but, unlike true mica, do not spring back to their original shape when released, a simple field test that separates the two groups without any equipment.
How to identify Chlorite
Chlorite appears as dull to pearly green flakes, scales, or earthy coatings, occasionally forming pseudohexagonal crystals in metamorphic rocks. It has one perfect cleavage direction like mica, but the resulting flakes are flexible without being elastic, meaning they do not snap back when bent. Hardness is low, around 2 to 2.5, and streak is pale green to colorless. This flexible-but-inelastic cleavage is the key test separating chlorite from biotite mica, which looks similar but springs sharply back into shape.
- Compare the specimen's color, luster, crystal habit, grain size, streak, and locality before confirming.
- Use multiple photos when possible, including a fresh surface and a close view of texture.
Where Chlorite is found
Reported from multiple localities worldwide; verify locality against specimen provenance when available.
How much is Chlorite worth?
| Entry-level specimen | $2 |
|---|---|
| Typical collector specimen | $20 |
| Premium specimen | $150+ |
Value depends on size, crystal quality, color, locality, rarity, damage, and provenance.
Common uses
- Collector specimens
- Education
- Field identification
- Industrial or lapidary use when suitable
Interesting facts
- Chlorite's cleavage flakes bend easily but never spring back, the classic hand-lens test that separates it from true micas.
- It gives many metamorphic rocks, including greenschist and greenstone, their characteristic dull green color.
- Chlorite commonly forms by altering darker minerals like biotite and pyroxene, effectively recording a rock's cooling and alteration history.
Care & safety
Handle as a collector specimen until hardness, cleavage, and fracture are verified.
Avoid inhaling dust. Do not cut, grind, or polish unknown specimens without eye protection and a proper respirator.
.jpg?width=320)
.jpg?width=320)