Leonard James Spencer

“ Well-developed crystals are of frequent occurrence. They usually have the form of four- or eight-sided prisms terminated by the basal planes (c) and pyramid-planes (p in fig.) ; the prism-planes are vertically Striated and the basal planes smooth and bright. Crystals are transparent to translucent, vitreous in lustre and vary in colour from brown to green; a sky-blue variety, called cyprine, owes its colour to the presence of a trace of copper. The specific gravity is 3.4 and the hardness . ”