In the paper, an oblique rectilinear central crack opening in an uniaxially tensile plane with a mixed mode of fracture (combination of normal separation and longitudinal shear modes) in two types of anisotropic materials (orthotropic one and one with cubic symmetry) has been studied. Stress intensity coefficient values for different crack orientations were calculated using expressions derived from the Lekhnitskii formalism and extrapolated methods for displacements and stresses. The results of verification of the used approach based on comparison of the finite element calculation with analytical one were presented (the difference was less than 0.75 %). A comparative analysis of the stress intensity and crack opening coefficients for three types of symmetry of elastic properties: isotropic material, material with cubic symmetry and orthotropic material was carried out.