The angle (recip-beta) defining the reciprocal cell in degrees.
               (recip-alpha), (recip-alpha) and (recip-alpha) related to the
               angles in the real cell by:
               cos(recip-alpha)
                   = [cos(beta)*cos(gamma) - cos(alpha)]/[sin(beta)*sin(gamma)]
               cos(recip-beta)
                   = [cos(gamma)*cos(alpha) - cos(beta)]/[sin(gamma)*sin(alpha)]
               cos(recip-gamma)
                   = [cos(alpha)*cos(beta) - cos(gamma)]/[sin(alpha)*sin(beta)]
               Ref: Buerger, M. J. (1942). X-ray Crystallography, p. 360.
                       New York: John Wiley & Sons Inc.