Leonard James Spencer, 1911 Encyclopædia Britannica, Volume 13… (1911)
“ A common and characteristic form of twinned crystal, such as is represented in the figure, consists of four intercrossing individuals twinned together according to two twin-laws; the compound group resembles a tetragonal crystal with prism and pyramid, but may be distinguished from this by the grooves along the edges of the pseudo-prism. The faces of the crystals are marked by characteristic striations, as indicated in the figure. Twinned crystals of exactly the same kind are also frequent in phillipsite (q.v.) . Crystals are usually white and translucent, with a vitreous lustre. ”
