"Inosilicates": Chain silicates 
Single chain silicates = "Pyroxenes" and Pyroxenoids - SiO₃

Each tetrahedron shares a total of 2 oxygens with 2 different neighboring tetrahedra:


Si:O ratio is 1 : 3

Examples of Pyroxenes: 


Enstatite MgSiO₃ 
Hypersthene (Mg,Fe)Si0₃ 
Ferrosilite FeSi0₃

Augite (Ca,Na)(Mg,Fe,Al)(Si,Al)₂O₆ 
Diopside CaMgSi₂0₆ 
Hedenbergite CaFeSi₂0₆

Also click here for a triangular compositional diagram of the pyroxenes

*In PYROXENES the chains are untwisted and extend along the c-axis*

Pyroxenes are subdivided into two groups: 
Orthopyroxenes - do not contain Ca - contain smaller cations so both the M1 and M2 cation sites are in 6CN. This results in a Orthorhombic crystal structure.

Clinopyroxenes - contain Ca (which is a large cation) along with smaller cations - the M1 site is a 6CN site that takes the smaller cations, whereas the M2 site becomes a 7-8CN site to accommodate the large Ca ions. This results in a lower symmetry, and a Monoclinic crystal structure.

*In PYROXENOIDS the chain structure is twisted, resulting in a lower symmetry (triclinic system) and longer repeat distances*

Examples of Pyroxenoids: 


Wollastonite CaSiO₃ 
Rhodonite MnSiO₃

Single chain inosilicates display 2 good cleavages at 87° and 93°

 

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