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The Mica Group of Minerals

The Mica Group Members Are

The True Micas

Dioctahedral
Aluminoceladonite (Potassium Aluminum Magnesium Iron Silicate Hydroxide)
Boromuscovite (Potassium Boro-silicate Hydroxide)
Celadonite (Potassium Iron Magnesium Silicate Hydroxide)
Chromphyllite (Potassium Chromium Aluminum Silicate Hydroxide Fluoride)
Ferro-aluminoceladonite (Potassium Aluminum Iron Magnesium Silicate Hydroxide) Ferroceladonite (Potassium Iron Magnesium Silicate Hydroxide)
Muscovite (Potassium Aluminum Silicate Hydroxide) Variety: Fuchsite
Nanpingite (Cesium Aluminum Silicate Hydroxide)
Paragonite (Sodium Aluminum Silicate Hydroxide)
Roscoelite (Potassium Vanadium Aluminum Silicate Hydroxide)
Tobelite (Ammonium Aluminum Silicate Hydroxide)

Trioctahedral
Annite (Potassium Iron Aluminum Silicate Hydroxide)
Aspidolite (Sodium Magnesium Aluminum Silicate Hydroxide)
Biotite (Potassium Magnesium Iron Aluminum Silicate Hydroxide Fluoride)
Eastonite (Potassium Magnesium Aluminum Silicate Hydroxide)
Ephesite (Sodium Lithium Aluminum Silicate Hydroxide)
Hendricksite (Potassium Zinc Aluminum Silicate Hydroxide)
Lepidolite (Potassium Lithium Aluminum Silicate Fluoride Hydroxide)
Masutomilite (Potassium Lithium Aluminum Manganese Silicate Fluoride)
Montdorite (Potassium Iron Manganese Magnesium Aluminum Silicate Fluoride)
Norrishite (Potassium Lithium Manganese Silicate)
Polylithionite (Potassium Lithium Aluminum Silicate Fluoride)
Phlogopite (Potassium Magnesium Aluminum Silicate Hydroxide)
Preiswerkite (Sodium Magnesium Aluminum Silicate Hydroxide)
Siderophyllite (Potassium Iron Aluminum Silicate Hydroxide)
Tainiolite (Potassium Lithium Magnesium Silicate Fluoride)
Tetra-ferri-annite (Potassium Iron Silicate Hydroxide)
Tetra-ferriphlogopite (Potassium Magnesium Iron Silicate Hydroxide)
Trilithionite (Potassium Lithium Aluminum Silicate Fluoride)
Zinnwaldite (Potassium Lithium Iron Aluminum Silicate Fluoride Hydroxide)

The Brittle Micas

Dioctahedral
Chernykhite (Barium Vanadium Aluminum Silicate Hydroxide)
Margarite (Calcium Aluminum Silicate Hydroxide)

Trioctahedral
Anadite (Barium Potassium Iron Magnesium Aluminum Silicate Hydroxide)
Bityite (Calcium Lithium Aluminum Beryllium Silicate Hydroxide)
Clintonite (Calcium Magnesium Aluminum Silicate Hydroxide)
Kinoshitalite (Barium Magnesium Aluminum Silicate Hydroxide)

The Interlayer-deficient Micas

Dioctahedral
Brammallite (Sodium Aluminum Silicate Hydroxide)
Glauconite (Potassium Sodium Iron Aluminum Magnesium Silicate Hydroxide)
illite (Potassium Aluminum Silicate Hydroxide)

Trioctahedral
Wonesite (Sodium Magnesium Aluminum Silicate Hydroxide)

The mica group is a group of related minerals that contain aluminum silicate. Micas are composed of sheets of silicate tetrahedrons. The silicate sheets are composed of inter connected six membered rings. These rings are responsible for mica's typical six sided pseudohexagonal symmetry. The percentage of its component elements may vary, which causes many people not to recognize the micas as a series.

The micas are soft and have perfect basal cleavage, which is seen when a mica is "peeled". The mica group is in the phyllosilicates subdivision of the silicates group. The micas are significant rock forming minerals being found in all three rock types: igneous, metamorphic and sedimentary.

The three most common mica minerals are muscovite, biotite, and lepidolite. A few of the less common micas that may be seen as mineral specimens are glauconite, paragonite, phlogopite and zinnwaldite. The Mica Group is a rather large group of minerals with over 30 members.

The Mica Group minerals are closely associated with the clay minerals. The clays have a similar structure but include brucite and gibbsite layers between their silicate layers. Sometimes the mica and clay layers are mixed forming a composite crystal. This can make identification and classification confusing. The mica minerals muscovite, glauconite and illite are often considered clays due to their clay like properties.

There are three major divisions within the Mica Group; The True Micas, The Brittle Micas and a new division called The Interlayer-deficient Micas.

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