Prehnite

This specimen came from the same place as the last, and leads to a curious modification. The crystals are arranged in double stellated groups, the radii of each extending so as to meet at the edges, like the spokes of two wheels placed against each other, contrary to their position on carriages; the periphery of the wheels coming together; the edges forming one circular face ; see the left- and right-hand figures. These are grouped among roughish indistinct semi-orbicular masses. The colour is not so attracting as the formation, being dull and brownish. This mineral is formed in the cavities of Kragg rock somewhat approaching Porphyry. The crystals are nearly similar to those of tab. 193, but the secondary faces being larger, the terminal one is lost in an edge.