It is shown that a general penny-shaped crack situated in a basal plane of a hexagonal crystal can be studied in a straightforward way using the corresponding results appropriate to an isotropic medium. The stress intensity factors are derived, and discussed for the case in which the crack is subjected to a unidirectional shear traction.We shall consider an infinite body composed of linearly elastic material of hexagonal symmetry containing a penny-shaped crack situated in a basal plane. Taking axes in such a way that the basal planes are normal to the z-axis, we shall suppose that the crack occupies the region z= 0, 0 < r < c, where (r, 0, z) £orm a system of cylindrical polar coordinates. We consider the problem in which the crack is loaded by means of tractions applied to its two faces, so that arz(r, 0, 0), aoz(r, 0, 0) and o-zz(r, 0, 0) are prescribed for 0 < r < c, where we use aij (r, O, z) to denote the/j-component of stress at the point (r, 0, z). No loading is applied at infinity, so that o-ij~0 as r2+z2~oc.This general penny-shaped crack problem, but in an isotropic body, has been solved by Guidera and Lardner [1] by regarding the crack as a Somigliana dislocation. If we denote by Au~(r, O) the components of the displacement discontinuity across the crack--i.e. Aui(r, O) = ui(r, O, O+)-ui(r, 0, 0-) (r