Leonard James Spencer, 1911 Encyclopædia Britannica, Volume 25… (1911)
“ It frequently occurs as well-formed crystals, which are orthorhombic and occasionally show signs of hemimorphism: they have the form of six-sided prisms or flat tables terminated by large basal planes and often modified at the edges by numerous pyramid-planes. Twinning on the prism-planes is of frequent occurrence, giving rise to pseudo-hexagonal groups like those of aragonite. ”
