Nenadkevichite Locality: Poudrette quarry (Demix quarry; Uni-Mix quarry; Desourdy quarry), Mont Saint-Hilaire , Rouville RCM, Montérégie , Québec , Canada ( Locality at mindat.org ) This specimen contains what are by far and away among the largest reported crystals of the species, as do other specimens from the remarkable find which are shown below. These crystals are to 6-8 mm in size and are nice and fat as well. Previous examples have usually been at the 1-2mm size level or less! The matrix was extremely loose in the pocket and so nearly all recovered specimens are thumbnails (from which I cherrypicked the best 10 or so - below). This was one of the two best larger specimens of Nenadkevichite which I was able to obtain from Gilles Haineault , which were collected by him in July of 2003. However, with delays for prep and analysis, I only heard about these amazing specimens this summer. The identity has been solidly confirmed and they stand as exceptionally beautiful and significant examples of the species. 4.4 x 3.4 x 2.0 cm — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Nenadkevichite
A rare niobium-bearing silicate forming brown-to-rose orthorhombic crystals in alkaline rocks.
Intro adapted from Wikipedia (CC BY-SA).
Nenadkevichite is an IMA-recognized mineral species in the silicate class, with the chemical formula (Na, )₈Nb₄(Si₄O₁₂)₂(O,OH)₄·8H₂O.
It crystallizes in the monoclinic crystal system (space group Cm). It is a member of the Labuntsovite structural group.
Key properties: Mohs hardness 5; specific gravity 2.78–2.88; White to very pale rose streak; Vitreous to dull luster; optically biaxial.
IMA symbol Nkv, grandfathered status — known before the IMA’s founding, named in 1955.
Between crystals of microcline in a natrolite-albite-rich pegmatite in nepheline syenite in a differentiated alkalic massif (Lovozero massif, Russia); in pegmatites, cavities in igneous breccia, hornfels.
It is found associated with Microcline (Lovozero massif, Russia); microcline, aegirine, catapleiite, ancylite, epididymite, eudialyte, s¶erandite, pectolite, apophyllite, monteregianite.
The name refers to Konstantin Avtonomovich Nenadkevich (1880–1963), Russian mineralogist and geochemist, A.E. Fersman Mineralogical Museum, Moscow, Russia.