Kaolinite subgroup

Kaolinite (triclinic) Al₄[(OH)₈/Si₄O₁₀]

	Colour: colourless Pleochroism: non pleochroic Habit: It usually occur as fine-grained aggregates in flour-like and clay-like masses. Masses are formed by very tiny plates (15-3µm) Relief: low positive Cleavage, fracture: perfect, one direction cleavage.
	Isotropic or anisotropic: anisotropic Extinction: inclined Interference colours: 1st order, grey

Mica minerals

Muscovite (monoclinic) KAl₂[(OH,F)₂/AlSi₃O₁₀]

	Colour: colourless Pleochroism: non pleochroic Habit: platty Relief: positive Cleavage, fracture: perfect, one direction cleavage. Inclusions: occasionally Zircon inclusions
	Isotropic or anisotropic: anisotropic Extinction: nearly straight at 87º Interference colours: 2nd order Distinguished features: intergrowths of Muscovite and Biotite

Sericite

	Is a fine grained Muscovite or Paragonite. Sericite is a common alteration of feldspars in areas that have been subjected to hydrothermal alteration.
	I

Biotite (monoclinic) K(Mg,Fe²⁺,Fe³⁺,Al,Ti)₃[(OH,F)₂/Al(Si,Al)Si₂O₁₀]

	Colour: brown, green Pleochroism: strong pleochroism Habit: platty Relief: positive Cleavage, fracture: perfect, one direction cleavage. Inclusions: common Zircon inclusions Alternations: Chlorite minerals are common alternation of Biotite
	Isotropic or anisotropic: anisotropic Extinction: nearly straight at 87º Interference colours: 2nd/3rd order Distinguished features: intergrowths of Biotite and Muscovite

Chlorite minerals (monoclinic) (Fe, Mg, Al.)₆[(OH)₂/(Si, Al.)₄O₁₀]

	Clinochlore (Mg,Fe2+)5Al[(OH)8[AlSi3O10] Pennine (Mg,Al)6[(OH)2/AlSi3O10] Colour: green Pleochroism: strong pleochroism Habit: platty Relief: positive Cleavage, fracture: perfect, one direction cleavage. Alternations: Chlorite minerals are common alternation of Biotite
	Isotropic or anisotropic: anisotropic Extinction: inclined Interference colours: subnormal (purple, brown)

Hydromicas

Glauconite (K,Na,Ca)(Fe,Al,Mg,Fe)₂[(OH)₂/(Al,Si)₄O₁₀] x nH₂O

	Colour: green Pleochroism: weak pleochroism Habit: fine grained aggregates, rounded pellets Relief: low positive (grains are flat) Cleavage, fracture: perfect, one direction cleavage.
	Isotropic or anisotropic: anisotropic Extinction: inclined Interference colours: 2nd order (blue, green)