![]() All network solids are different on the inside than they are on the outside. The inosilicate chain drawn above does illustrate an important consideration that it has in common with network solids. In the polyhedral drawing, the repeating units are simply tetrahedra. They contain individual units that keep repeating all along the chain. In a sense, inosilicates could also be described as polymers. There could be hundreds of silicate units in a row. However, at least in one direction, they are covalently bonded and can extend indefinitely. Inosilicates are not exactly network solids because they do not form three-dimensional networks. The polyhedral drawing of a section of inosilicate ion is shown below. Materials containing these long chain silicates are called inosilicates ("sinew" or "string" silicates). The same is true in the next unit, and so on, forming a long chain. To do so, two of the oxygens in a silicate unit have to be shared with two other silicate units. If two silicate units can share an oxygen, more can, too. We are looking at the top of one tetrahedron but the bottom of the other one. In the picture on the right we are looking at it from a different angle to emphasize that the two tetrahedra are pointing in opposite directions. In the picture on the left, we are looking at it from the same angle as the orosilicate shown above. The different shapes that result are called "conformations". It contains two units that can twist relative to each other. ![]() The sorosilicate anion can actually adopt different shapes in different cases. It contains nesosilicate, sorosilicate, oxide and hydroxide anions, as well as calcium, iron and aluminum cations. It could be a number of colors but is usually green. For example, epidote is a more common form of sorosilicate-containing mineral. In some minerals, they are even found in combination with nesosilicates. Where they exist, sorosilicates are found in the presence of other anions, as well as cations. Sorosilicates are not nearly as common as nesosilicates. They just contain slightly bigger anions than nesosilicates. Sorosilicates clearly aren't network solids, either. In the polyhedral depiction, the two tetrahedra share a corner. The two silicate units share an oxygen atom. Sorosilicates ("sister" silicates) are silicate anion dimers. These two counterions are always present in a 3:2 ratio in garnet. One of them is a M 2+ ion and the other is a M 3+ ion (M here just stands for "metal"). Garnets always contain two different cations. There are many kinds of garnet, but a common one is almandine, the red-brown color of which we usually think of as "garnet". Garnets are used as gems as well as abrasives - they are sometimes used in sandpaper.
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