Editing Pyroxene (section)

==Structure==
Pyroxenes are the most common single-chain silicate minerals. (The only other important group of single-chain silicates, the [[pyroxenoid]]s, are much less common.) Their structure consists of parallel chains of negatively-charged silica tetrahedra bonded together by metal cations. In other words, each silicon ion in a pyroxene crystal is surrounded by four oxygen ions forming a tetrahedron around the relatively small silicon ion. Each silicon ion shares two oxygen ions with neighboring silicon ions in the chain.<ref name=Nesse2000p261>{{cite book |last1=Nesse |first1=William D. |title=Introduction to mineralogy |date=2000 |publisher=Oxford University Press |location=New York |isbn=9780195106916 |page=261}}</ref>

The tetrahedra in the chain all face in the same direction, so that two oxygen ions are located on one face of the chain for every oxygen ion on the other face of the chain. The oxygen ions on the narrower face are described as apical oxygen ions. Pairs of chains are bound together on their apical sides by Y cations, with each Y cation surrounded by six oxygen ions. The resulting pairs of single chains have sometimes been likened to [[I-beam]]s. The I-beams interlock, with additional X cations bonding the outer faces of the I-beams to neighboring I-beams and providing the remaining charge balance. This binding is relatively weak and gives pyroxenes their characteristic [[cleavage (mineralogy)|cleavage]].<ref name=Nesse2000p261/>
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File:Ino a.jpg|A single chain of silicon tetrahedra viewed in the [100] direction
File:Ino b.jpg|A single chain of silica tetrahedra viewed in the [010] direction
File:Diopside c scaled ibeam.jpg|Structure of pyroxene looking along the silica chains. "I-beams" are outlined in green. Silicon ions are oversized to emphasize the silicon chains. 
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