Crystal Chlorite

Chemical Formula

Below is a simple formula encompassing the common members of the Chlorite Group:
(Mg,Fe,Li)₆AlSi₃O₁₀(OH)₈

The formula for the three most common individual group members are:
Cookeite: LiAl₅Si₃O₁₀(OH)₈
Clinochlore: (Mg,Fe²⁺)₅Al₂Si₃O₁₀(OH)₈
Chamosite: (Fe²⁺,Mg)₅Al₂Si₃O₁₀(OH)₈
 

Composition

Basic iron magnesium aluminum silicate
 

Color

Light to dark green, grayish-green, black. Some rarer varieties are white, yellow, brown, pink and purple.

Streak

White

Hardness

2 - 2.5

Crystal System

Monoclinic

Crystal Forms 
and Aggregates

Crystals are usually tabular and pseudohexagonal in shape, but also may be prismatic. Also as thick flakes, micaceous masses and groupings, and in foliated, flaky, and scaly forms. May also be massiveand in globular masses of dense flakes.

Chlorite commonly form pseudomorphs and dense coatings of other minerals, assuming the original minerals crystal shape.

Transparency

Transparent to translucent

Specific Gravity

2.6 - 3.3

Luster

Vitreous, pearly, or dull

Cleavage

1,1

Fracture

Uneven

Tenacity

Thin flakes are flexible but not elastic.

Other ID Marks

Has a slightly greasy feel.
 

In Group

Silicates; Phyllosilicates; Chlorite Group

Striking Features

Color and lack of elasticity

Environment

Most often in metamorphic environments, especially in Serpentine deposits; also as a secondary mineral in volcanic basalt and in hydrothermal replacement deposits.
 

Rock Type

Igneous, Metamorphic

Popularity (1-4)

2

Prevalence (1-3)

1

Demand (1-3)

3