"Inosilicates": Chain silicates 
Double chain silicates = "Amphiboles" - Si₄O₁₁

Tetrahedra alternate sharing 2, then 3, then 2, then 3... oxygens with neighboring tetrahedra:


Si:O ratio is 4 : 11

Examples of Amphiboles: 


Hornblende (Ca,Na)_2-3(Mg,Al,Fe)₅Si₆(Si,Al)₂O₂₂(OH)₂ 
Tremolite Ca₂Mg₅Si₈O₂₂(OH)₂ 
Actinolite Ca₂(Mg,Fe)₅Si₆(Si,Al)₂O₂₂(OH)₂ 


Also click here for a triangular compositional diagram of the amphiboles

• In the structure of double chain inosilicates, the two linked chains have a large "hole" between them
  - this hole is filled by large anions like OH^-, Cl^-, F^-

  - water (OH^-) is common in the holes at lower temperatures but can be driven out of structure with heating

  - when the water is driven out, the structure may convert to a pyroxene

   

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