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A total of 32 synthetic end-member and solid-solution compounds of the LiM 3+ Si 2 O 6  (Li = M2 site, M 3+  = M1 site = Al, Ga, V, Fe, Sc and In) clinopyroxene series have been investigated by single-crystal X-ray diffraction. Except LiCrSi 2 O 6 , all compounds show  C 2/ c  symmetry at 295 K. LiCrSi 2 O 6  has space group  P 2 1 / c  but transforms to the high temperature  C 2/ c  structure at 335 K. The variations of structural parameters in the LiMe 3+ Si 2 O 6  clinopyroxenes are dominated by the Me 3+  site. The average M1—O bond length is linearly correlated with the ionic radius of the M1 cation. Octahedra reflect the increasing size of the M1 cations by steadily increasing bond and edge lengths, the variations however are not uniform. With increasing size of the M1 cation, octahedra deviate from ideal octahedral geometry. Octahedral edges, shared with other structural units, are distinctly hampered in expansion with increasing size of the M1 cation. The increasing size of the M1 octahedral chain is compensated by changing the kinking of the tetrahedral chain and by alterations of bond and edge lengths as well as the bond angles within the tetrahedron. Three different mechanisms of adapting of the structural building units with increasing M 3+  cationic radius can be identified: (i) expansion of the tetrahedral chain by stretching (ii) transition form “O” to “S” chain conformation after full expansion and (iii) finally a limit of expansion in  a  direction. We stress that cations larger than In 3+  cannot be substituted at the M1 site because of too large geometrical differences between octahedral and tetrahedral chains.

Structural variation and crystal chemistry of LiMe 3+ Si 2 O 6 clinopyroxenes Me 3+ = Al, Ga, Cr, V, Fe, Sc and In