These crystals were noted early in investigations, and were thought of as aragonite sixlings. However Ruth Jacobsen sent some specimens to William Henderson who wrote up the mineral in the Mineralogical Record, Vol 14, No 1, 1983. “It was immediately sight-identifiable as erionite, being identical in crystal form to that from a number of localities in the American Southwest. The optics fit erionite exactly. The optically clear crystals are simple in habit, showing only the hexagonal prism and base. The terminal faces sometimes show interesting growth spirals in irregular circular patches, with up to three such spirals on a single face. The crystals are really fine.“
The crystals are really clear and difficult to see unless the light catches them. They occur as fat singles, radiating groups, generally on the vugh surface, or surrounded by chabazite clusters.
Below: Erionite-K, phillipsite-K, Moeraki Point, Otago, New Zealand. Width of view 5.75mm.
