  We report the first-principle FLAPW-GGA calculations of the elastic
properties of two related layered phases, namely, the ternary arsenide SrFe2As2
and the quaternary oxyarsenide LaFeAsO - basic phases for the newly discovered
"122" and "1111" 38-55K superconductors. The independent elastic constants
(Cij), bulk moduli, compressibility, and shear moduli are evaluated and
discussed. The numerical estimates of the elastic parameters of the
polycrystalline SrFe2As2 and LaFeAsO ceramics are performed for the first time.
Additionally, the peculiarities of chemical bonding in these phases are
discussed.
