The important species of chlorite groups ate as follows

These are micaceous minerals which are green in colour and have cleavage flakes which are flexible but not elastic. They are devoid of alkali metals and rich in ferrous iron. They show a type of sheet structure and are hydrous. The important species of chlorite groups ate as follows:

1. Clinochlore. 2. Penninite. 3. Prochlorite.

Physical properties:

(i) They all crystallise in the monoclinic system.

(ii) Cleavage. Perfect,

(iii) Hardness- 1 to 2.5.

(iv) Sp. gravity. 2.5 to 3.

(v) Twinning. Not ecognizable in handspecimen.

Optical properties:

(a) Green in colour and pleochroic.

(b) Ref. index. Higher than Canada Balsam.

(c) Birefringence. Very weak=0.001 to O.O11.

(d) Interference colour. First order.

(e) Extinction. Parallel.

Variety:

1. Chamosite:

An iron-rich chlorite.

2. Chlorophaeite:

A chlorite formed by the alteration of voIcanic glass.

Occurrence:

These are always secondary resulting by the metamoiphism or hydrothermal alteration of ferromagnesian minerals.