Scolecite - Encyclopedia

    Class : Silicates
    Subclass : Tectosilicates
    Crystal system : Monoclinic
    Chemistry : CaAl2Si3O10 3H2O
    Rarity : Fairly common


Scolecite belongs to the group of zeolites, hydrated aluminosilicates made up of a framework crisscrossed with channels in which water and large cations are inserted. Scolecite is one of the most abundant zeolites with natrolite and mesolite from which it is difficult to distinguish. The crystals have the same appearance as those of natrolite and mesolite : very elongated prisms, forming divergent aggregates or clumps of extremely fine crystals. Transparent to translucent, with a vitreous to silky sheen for finely fibrous masses, it is colorless to white, rarely yellowish or orange. It is mainly found in basalt cavities, associated with apophyllite, calcite, natrolite and many other zeolites. It is rarer in alpine slits in crystalline schists or alkaline plutonic rocks. It is a mineral occasionally cut into cabochon.

Twinned scolecite from India
Spray of scolecite from Mumbai, India
26.50 ct scolecite cabochon from India
40.61 ct scolecite cabochon from India

Scolecite in the World

The finest samples of scolecite come from the quarries of Khandivali, near Mumbai, and Nasik (India): it forms large striated prisms with often acicular terminations (up to 30 cm), or divergent groups of colorless crystals with neat endings reach 20 cm in diameter. In the same context of the Deccan traps, the Poona quarries yielded colorless crystals up to 35 cm by 2 cm, forming sheaves with stilbite and laumontite.

Brazil, with the site of Das Antas (Rio Grande do Sul), gave magnificent colorless crystals grouped in clusters, associated with the apophyllite. The classic deposits of New Jersey (United States) and the Bay of Fundy (Nova Scotia, Canada) have given excellent specimens, as have the basalts of Berufjord (Iceland) whose cavities conceal tufts of crystals up to 10 cm. Note also that the basalt cavities of Mount St-Helens (Washington) present needle crystals of 14 cm by 15 mm.

The Swiss Alpine Slits (Val Calanca and Val Giuv in Graubünden) also contain magnificent tufts of crystals but of more modest dimensions (3 cm), associated with epidote and prehnite.

Scolecite in France

In France, scolecite is known in the basalts of Gergovie (Puy-de-Dôme), at the Pic du Midi (Pyrenees), and in the alpine slits around Chamonix (Haute-Savoie).

Twinning

Twinning is common on {100} by contact or penetration. The crystals then appear as a spearhead.

Fakes and scams

No false recorded for this mineral species, but can be easily confused with other zeolites with which it shares the deposits.



Hardness : 5 to 5.5
Density : 2.25 to 2.29
Fracture : Conchoidal
Trace : White



TP : Translucent to transparent
RI : 1.507 to 1.521
Birefringence : 0.010
Optical character : Biaxial -
Pleochroism : None
Fluorescence : None


Solubility : Acids

Magnetism : None
Radioactivity : None