The Milarite - Osumilite Group of Minerals

The Milarite - Osumilite Group is sometimes simply called the Osumilite Group, but it is also sometimes called the Milarite Group. It is a group of similarly structured cyclosilicates. The primary structural unit of this group is a most unusual double ring, with a formula of Si₁₂O₃₀. Normal rings of cyclosilicates are composed of six silicate tetrahedrons; with a formula of Si₆O₁₈. The double ring is made of two normal rings that are linked together by sharing six oxygens, one from each tetrahedron in each six membered ring (notice the loss of six oxygens in the double ring formula). The structure is analogous to the dual wheels of a tractor trailer.

The general formula for this group is X_1-2Y_2-3Z₃(Si, Al)₁₂O₃₀ - 0-2H₂O. The X ion can be either calcium, potassium, sodium and/or barium. The Y ion can be either iron, lithium, yttrium, magnesium, manganese, sodium, tin, titanium, zinc and/or zirconium. The Z ion can be either aluminum, beryllium, iron, lithium, magnesium and/or boron. Some members contain no aluminum ions or water molecules.

The Milarite - Osumilite Group is composed of rather rare minerals. Only sugilite, milarite and osumilite are somewhat well known minerals from this group. All others are very rare to extremely rare in occurrence.

• Armenite (Hydrated Barium Calcium Aluminum Silicate)
• Berezanskite (Potassium Lithium Titanium Silicate)
• Brannockite (Potassium Lithium Tin Silicate)
• Chayesite (Potassium Magnesium Iron Silicate)
• Darapiosite (Potassium Sodium Lithium Manganese Zinc Zirconium Silicate)
• Dusmatovite (Potassium Sodium Manganese Yttrium Zirconium Zinc Lithium Silicate)
• Eifelite (Potassium Sodium Magnesium Silicate)
• Emeleusite (Sodium Lithium Iron Silicate)
• Merrihueite (Potassium Sodium Iron Magnesium Silicate)
• Milarite (Hydrated Potassium Calcium Aluminum Beryllium Silicate)
• Osumilite (Hydrated Potassium Sodium Iron Magnesium Aluminum Silicate)
• Osumilite-(Mg) (Hydrated Potassium Sodium Magnesium Iron Aluminum Silicate)
• Poudretteite (Potassium Sodium Boro-Silicate)
• Roedderite (Sodium Potassium Magnesium Iron Silicate)
• Shibkovite (Potassium Calcium Manganese Sodium Lithium Iron Zirconium Titanium Silicate)
• Sogdianite (Potassium Sodium Lithium Aluminum Iron Titanium Zirconium Silicate)
• Sugilite (Potassium Sodium Lithium Iron Manganese Aluminum Silicate)
• Yagiite (Sodium Potassium Magnesium Aluminum Iron Silicate)