Silicate minerals are made up of various elements in combination with silicon and oxygen, both of which are also elements. They're very common, and comprise 75 percent of all common minerals, according to Missouri State University. They are very common in Earth's crust, and have even been found on Mars, according to Nature.com.
Cyclosilicates consist of closed rings made up of tetrahedral arrangements of atoms. The cyclosilicates include a variety of different minerals, including several that are commonly considered to be gemstones. For instance, emerald and tourmaline are both cyclosilicate minerals. The cyclosilicates all have a 1:3 ratio of silicon atoms to oxygen atoms, notes Missouri State University, which is one of the higher ratios of silicon to oxygen among the silicate minerals.
Inosilicates are made up of tetrahedral arrangements of silicon and oxygen atoms arranged into long chains. Each tetrahedron has a silicon atom at the center, bonded to four different oxygen atoms that form the corners of the tetrahedral shape. Where a tetrahedron connects to the next tetrahedron in the chain, the silicon atoms in the two tetrahedrons share the corner oxygen. Common inosilicates include jadeite and rhodonite.
Phyllosilicates consist of sheets of connected tetrahedrons, where once again, each tetrahedral unit consists of a central silicon atom attached to four oxygen atoms. Because there is more extensive sharing of oxygen atoms due to increased bonding between tetrahedrons in phyllosilicates, the overall silicon to oxygen ratio is 2:5. Common phyllosilicates include clay minerals such as talc, various types of mica including muscovite, and unusual-appearing minerals like lizardite.
Sorosilicates and Neosilicates
While both sorosilicates and neosilicates, like the other silicate mineral subcategories, consist of the same tetrahedral arrangements of silicon and oxygen atoms, the linking between tetrahedrons is much less extensive in these two categories than in the other subcategories of silicate minerals. In sorosilicates, each tetrahedron is linked to only one other tetrahedron, resulting in a 2:7 overall ratio of silicon to oxygen. In neosilicates, there is no linking between silicon tetrahedrons, resulting in a 1:4 ratio of silicon to oxygen, which is the lowest possible ratio in a silicate mineral.