1911 Encyclopædia Britannica/Scolecite

by Leonard James Spencer

SCOLECITE, a mineral belonging to the zeolite group; a hydrated calcium silicate, CaAl₂Si₃O₁₀+3H₂O. It is a lime-zeolite, and like the soda-zeolite natrolite and the soda-lime-zeolite mesolite, usually occurs as acicular and fibrous aggregations. Although having nearly the same inter facial angles as the orthorhombic natrolite, it crystallizes in the monoclinic system, and, as shown by the etched figures and the pyroelectric character, in the hemihedral class of this system, there being a plane, but no axis, of symmetry. Scolecite can therefore be distinguished from natrolite by an optical examination, since the acicular crystals do not extinguish parallel to their length between crossed nicols. Twinning on the ortho-pinacoid is usually evident. The mineral is colourless or white, transparent, and vitreous in lustre: the hardness is 51/2, and the specific gravity 2.2. It is a mineral of secondary origin, and occurs with other zeolites in the amygdaloidal cavities of weathered volcanic rocks of basic composition. Fine divergent groups of prismatic crystals are found in the basalt of Berufjord near Djupivogr in Iceland and in the Deccan traps near Poona in India; hence the synonym poonahlite for this species. The name scolecite is derived from Gr. σκώληξ, a worm, because the crystals sometimes curl up like worms when heated before the blowpipe.  (L. J. S.)