Lustrous group of gmelinite pseudomorphs after chabazite, with the largest crystal measuring 2.7 cm. Associated with the gmelinite is a beautiful glassy clear analcime 4 mm across, and also minor tan heulandite. The backside of this piece illustrates how dissolved and spongey the texture of some of the chabazite from this find is (also includes some mineralogical oddities, which appear to possibly pseudomorphs of quartz after anhydrite and microscopic copper mineralization). The gmelinite is bright with great crystallization patterns, and the specimen is in excellent condition – one spot on the backside of a termination of the large crystal may be dissolution or chipping, very hard to say, but in any event it is not distracting. From Terry Collett, collected in July, 2006. A great gmelinite!
About These Gmelinites
Truly great, display-quality specimens of gmelinite are known from very few localities worldwide. These specimens of gmelinite from Pinnacle Rock are exceptional for the mineral – brilliant glassy lustre, sharp, with fantastic, intricate crystallization patterns. The group of specimens in this update represents some of the finest quality gmelinite from Pinnacle Rock.
The mode of occurrence has been described as “gmelinite on chabazite” and also “gmelinite after chabazite”. These specimens are comprised of a crystallized layer of gmelinite over chabazite, so that the overall shape is the rhombohedral chabazite form. Most of these retain a chabazite core to some degree, although often the chabazite can be quite porous, and some specimens are partial epimorphs, where the original chabazite core area has at least partially dissolved away altogether, leaving hollow spaces inside the outer gmelinite crystal layer. Given the overall exterior chabazite form, they are “gmelinite pseudomorphs after chabazite”, however it is important to distinguish that these are not gmelinite as a mere replacement material: the beautiful crystallization of the gmelinite prominently displays morphological habits and growth patterns, and it is these brilliant gmelinite crystal growths and overgrowths that make these specimens special.
These specimens are gmelinite-Na, as analyzed by the RRUFF Project
Situated in the Five Islands, in the Bay of Fundy, this locality is a classic, described in reports in Canada and the U.S. dating back to the 19th century. Specimens from Pinnacle Island (albeit as “Pinnack Island”) are included in Victor Goldschmidt’s famous early 20th century Atlas der Krystallformen. Pinnacle Rock produced spectacular specimens in 2004 and 2006 (the specimens here were among them). Unfortunately, a major area where specimens were found has now collapsed into the Bay of Fundy and has been washed away by the sea.
If you are interested in reading more about the locality, or seeing photographs, have a look at Ronnie Van Dommelen’s great website about The Mineralogy of Nova Scotia
; also see Van Dommelen, R. and Collett, T., “An Introduction to Minerals in Nova Scotia and a Report on Recent Collecting” in Rocks and Minerals
81:1 (Jan/Feb 2006), pp. 54-61.