Niobokupletskite, Aegirine, Calcio-Ancylite-(Ce) Calcite over Rhodochrosite

This specimen consists of many sharp black prisms of aegirine intersecting through a section of microcline feldspar, much of it is covered in rhodochrosite rhombs with a coating of grey calcite. To add some complexity to the specimen’s mineralogical significance is the presence of calcio-ancylite-(Ce) crystals, a cerium-dominant rare earth carbonate that occurs as colourless grains on top of the calcite. In some of the nooks and crannies of the microcline are rare and delicate tufts of niobokupletskite. These fine, acicular crystals—classified as Type III—radiate outward in a distinctive broom-like habit, a form that earned the humorous nickname “witch’s broom astrophyllite” in Rocks & Minerals (Wight & Chao, 1986). The crystals range in colour from yellowish-brown to silvery-brown. Niobokupletskite was originally discovered and collected by Peter Tarassoff on July 12, 1970. While there is a secondary occurrence reported in India, it has not produced specimens of collector interest, making Mont Saint-Hilaire effectively the only source for quality material of this rare titanium-niobium silicate.

Together, this combination highlights the paragenetic complexity and rare element geochemistry for which Mont Saint-Hilaire is celebrated. The overall composition makes this a highly desirable specimen for collectors of rare species or Mont Saint-Hilaire minerals.