Scolecite

Scolecite is a tectosilicate mineral belonging to the zeolite group; a hydrated calcium silicate, CaAl₂Si₃O₁₀·3H₂O. Its name came from the Greek word, skolec = 'worm' because of its reaction to the blowpipe flame. It is a calcium zeolite, and like the sodium-zeolite natrolite and the sodium-calcium zeolite mesolite, usually occurs as acicular and fibrous aggregations. Although having nearly the same interfacial 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 nicol prisms. Twinning on the ortho-pinacoid is usually evident. The mineral is colorless or white, transparent, and vitreous in luster. It has a Mohs hardness of 5 and a specific gravity of 2.2.

Occurrence

It is a mineral of secondary origin, and occurs with other zeolites in the amygdaloidal cavities of weathered mafic volcanic rocks. Associated minerals include quartz, apophyllite, babingtonite, heulandite, stilbite and other zeolites. It was first described from Kaiserstuhl in Baden in 1813. Fine divergent groups of prismatic crystals are found in the basalt of Berufjord near Djupivogr in Iceland and in the Deccan Traps near Pune in India; hence the synonym poonahlite for this species. Other occurrences include Riverside County, California; Skye, Scotland and Santa Catarina, Brazil.

References

* [http://mineral.galleries.com/minerals/silicate/scolecit/scolecit.htm Mineral galleries]
* [http://mindat.org/min-3594.html Mindat]
* [http://webmineral.com/data/Scolecite.shtml Webmineral]