Chlorite
(Mg,Fe)₃(Si,Al)₄O₁₀(OH)₂·(Mg,Fe)₃(OH)₆ · Monoclinic · also called green mica
Chlorite gives greenschist its colour and its name. It looks like a green mica and peels like one, but its flakes are flexible rather than elastic — the one test that reliably separates the two.
Properties
- Mohs hardness
- 2–2.5
- Streak
- white, pale green
- Lustre
- vitreous, pearly, dull
- Colour
- Almost always a distinct green, ranging from pale olive to dark blackish green.
- Cleavage
- Perfect basal cleavage into flexible but inelastic flakes.
- Fracture
- Not applicable
- Specific gravity
- 2.6–3.3 (water = 1)
- Magnetism
- Not magnetic
- Acid test
- No reaction
- UV
- Not fluorescent
Tests that confirm chlorite
- Bent flakes stay bent — the opposite of mica, and the standard way to tell them apart.
- Green colour and a slightly soapy feel.
- Coats and stains other minerals green in metamorphic rock.
What chlorite gets confused with
Each of these is settled by one test. Run that test first.
Bend a flake: biotite springs back, chlorite does not.
Serpentine is massive and waxy rather than peeling into sheets.
Where it is found
Low-grade metamorphic rocks, altered volcanic rock, and as a green coating in veins.
Is it worth anything?
None, though chlorite inclusions produce collectible green 'phantom' quartz crystals.