kaolin

Key facts

Category

Phyllosilicate minerals

Group

Kaolinite- Serpentine group, kaolinite subgroup

Formula

Al 2 Si 2 O 5 (OH) 4 , or in oxide notation: Al 2 O 3 · 2SiO 2 · 2H 2 O

Ima symbol

Kln

Strunz classification

9.ED.05

Crystal system

Triclinic

Crystal class

Pedial (1) , (same H-M symbol )

Space group

P 1

Unit cell

a = 5.13 Å , b = 8.89 Å , c = 7.25 Å; α = 90° , β = 104.5°, γ = 89.8°; Z = 2

Color

White to cream, sometimes red, blue or brown tints from impurities and pale-yellow; also often stained various hues, tans and browns being common.

Crystal habit

Rarely as crystals, thin plates or stacked. More commonly as microscopic pseudohexagonal plates and clusters of plates, aggregated into compact, claylike masses.

Cleavage

Perfect on {001}

Tenacity

Flexible but inelastic

Mohs scale hardness

2–2.5

Luster

Pearly to dull earthy

Streak

White

Specific gravity

2.16–2.68

Optical properties

Biaxial (–)

via Wikipedia infobox