Constituent
- Name
- Illite
- IMA name
- Illite
- Class
- silicate mineral
- Compound type
- phyllosilicate
- Relevance
- main - major
- Arrangement
- single phase
- Mass fraction
- 1.0
- Formula
- $(K_{0.6-0.85})(Al,Mg)_2(Si,Al)_4O_{10}(OH)_2$
- Chemical formula
- K0.6-0.85(Al,Mg)2(Si,Al)4O10(OH)2
- Elemental formula
- (Al)1-3 (K)0.6-0.85 (Mg)0-1 (Si)3-4 O12 H2
- Isotope mixture type
- terrestrial abundance
- Composition comments
- Generally considered as K-deficient muscovite with more Si. Si and Al proportions are very variables and Mg is generally minor. Common impurities:Fe
- Oxides
-
Formula $Al_{2}O_{3}$ $K_{2}O$ $MgO$ $SiO_{2}$ $H_{2}O$ Mass fraction (%)
Strunz
- Class
- silicates (09)
- Division
- phyllosilicate (09.E)
- Family
- with mica sheets, composed of tetrahedral and octahedral nets (09.EC)
- Code
- 09.EC.60
Dana
- Major class
- silicates (VIII)
- Class
- phyllosilicate sheets of six-membered rings (71)
- Type
- with 2:1 layers (71.02)
- Group
- Mica group (Hydromica subgroup) (71.02.02d)
- Code
- 71.02.02d.02
- Phase type
- crystalline
- Crystal system
- monoclinic
- Crystal class
- prismatic
- Crystal class symbol
- 2/m (C2h)
- Crystal spacegroup
- C2/m
- Comments
- Illite has different polytypes: Illite-1M, Illite-1Md, Illite-2M1, Illite-2M2, Illite-3T
- Texture
- monocrystalline
- Molar mass
- 389.34 $g/mol$
- Density
- 2.6-2.9 $g/cm^3$
- Refringence type
- biaxial
- Refringence sign
- negative
- Birefringence
- 0.0300-0.0350
- Refraction index $n_{\alpha}$
- 1.535-1.57
- Refraction index $n_{\beta}$
- 1.555-1.6
- Refraction index $n_{\gamma}$
- 1.565-1.605
- Dispersion V
- none
- Color
- White,Gray-white, Silvery-white, Greenish-gray
- Diaphaneity
- translucent
- Luster
- earthy