Typically, screw-dislocation-driven growth will dominate when the supersaturation in the solution is relatively low, which is observed here when the solution was in its initial period of slow cooling. From classical theory of dislocation-driven crystal growth, the radius of the hollow channel r is related to the Burgers vector of dislocation b as r = µb 2 8π 2 γ where µ is the shear modulus, and γ is surface energy density. Here the Eshelby twist 47 is not included, since for this case, the outer radius of the needle-shaped crystals is significantly larger than the inner radius. The formula above indicates a comparatively small surface energy for this synthesis, since the crystal is grown from a polysulfide flux with similar composition.