Interesting Groupings Gemstones, Birthstones, etc. 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 Si 12 O 30 . The structure is analogous to the dual wheels of a tractor trailer.
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.