High-pressure crystal structures and compressibilities of bertrandite, beryl, and euclase.

Unit-cell parameters are reported for these minerals at various P up to 54 kbar. Bertrandite compression is highly anisotropic because of tetrahedral-bond bending along b, but not a and c. Beryl is less anisotropic, regardless of whether molecules of the pressurizing medium were too large to enter the structural channels. Euclase is least compressible in the direction of the chain of 3-member tetrahedral rings and most compressible along b. Be-O bonds are more compressible than Al-O or Si-O; bending of tetrahedral-bond angles contributes significantly to compressibility.-K.F.