Elongation in the Direction of the Orthogonal Axis
In some cases, the elongation of a crystal may be in the direction of the orthogonal axis, whose position is determined by the plane of symmetry. This crystal of the silicate mineral, Epidote, shows an example of this.
George Huntington Williams, Ph.D. Elements of Crystallography for Students of Chemistry, Physics, and Mineralogy (New York, NY: Henry Holt and Company, 1892)