ALLANITE	The Epidote Group of Minerals	EPIDOTE
ZOISITE	TANZANITE a variety of ZOISITE	ALLANITE

The Epidote Group minerals are silicates of the general formula A₂B₃(SiO₄)₃ (OH, F). The A ion can be calcium, cerium, lead, strontium and/or yttrium. The B ion can be aluminum, iron, vanadium, magnesium and/or manganese. In some Epidote Group minerals there is some substitution of oxygens for hydroxides on the silicate tetrahedrons producing a formula of A₂B₃Si₃O₁₁ (OH, F)₂. The structure of the Epidote Group minerals is composed of both SiO₄ groups and Si₂O₇ groups in equal proportions. Epidote Group minerals could be classified as nesosilicates but the higher organization of the Si₂O₇ groups places them in the sorosilicate subclass. Silicate tetrahedral oxygens in the formula are combined with aluminums such that, together, they form chains of interconnected octahedrons. The silicate groups share oxygens with these chains and completing the structure are the A ions and the left over B ions.

The epidote group is composed of a number of members, but only the mineral epidote is common. Zoisite is used as a gemstone (a variety known as tanzanite) and as an ornamental stone. Clinozoisite, piemontite and allanite are three other members that can be found in well rounded mineral collections.

These are the members of the Epidote Group of minerals:

Allanite-(Ce) (Cerium Calcium Yttrium Aluminum Iron Silicate Hydroxide)

Allanite-(Y) (Yttrium Cerium Calcium Aluminum Iron Silicate Hydroxide)

Androsite-(La) (Manganese Calcium Lanthanum Cerium Niobium Aluminum Silicate Oxide Hydroxide)

Clinozoisite (Calcium Aluminum Silicate Hydroxide)

Dissakisite-(Ce) (Calcium Cerium Lanthanum Magnesium Aluminum Silicate Hydroxide)

Dollaseite-(Ce) (Calcium Cerium Magnesium Aluminum Silicate Fluoride Hydroxide)

Epidote (Calcium Iron Aluminum Silicate Hydroxide)

Hancockite (Lead Calcium Strontium Aluminum Iron Silicate Hydroxide)

Khristovite-(Ce) (Calcium REE Magnesium Iron Aluminum Manganese Silicate Hydroxide Fluoride Oxide)

Mukhinite (Calcium Aluminum Vanadium Silicate Hydroxide)

Piemontite (Calcium Aluminum Manganese Iron Silicate Hydroxide)

Strontiopiemontite (Calcium Strontium Aluminum Manganese Iron Silicate Hydroxide Oxide)

Zoisite (Calcium Aluminum Silicate Hydroxide)