Nepheline
NaAlSiO4
Locality:
Mt Cavalluccio, Campagnano di Roma, Sacrofano Caldera, Rome Province, Latium, Italy
0.61 mm Nepheline crystal.
Collection & Photo: Matteo Chinellato
Nepheline, also called nephelite (from Greek: νεφέλη, “cloud”), is a feldspathoid that occurs in intrusive and volcanic rocks with low silica, and in their associated pegmatites. Nepheline crystals are rare and belong to the hexagonal system, usually having the form of a short, six-sided prism terminated by the basal plane. The unsymmetrical etched figures produced artificially on the prism faces indicate, however, that the crystals are hemimorphic and tetartohedral, the only element of symmetry being a polar hexad axis.
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