NIVEOLANITE, THE FIRST NATURAL BERYLLIUM CARBONATE, A NEW MINERAL SPECIES FROM MONT SAINT-HILAIRE, QUEBEC, CANADA

Abstract

A new mineral species, niveolanite, the first natural carbonate of beryllium, was found in the Poudrette pegmatite, Poudrette quarry, Mont Saint-Hilaire, Quebec, Canada. It is associated with albite, aegirine, natrolite, gonnardite, siderite, petersenite-(Ce), franconite, dawsonite, analcime, quartz, eudidymite, catapleiite, gaidonnayite, monazite-(Ce), calcite, adamsite-(Y), shomiokite- (Y), galena, sphalerite and rutile in cavities; earlier minerals are microcline, nepheline, annite, sodalite and zircon. Niveolanite occurs as soft fibrous (random, matted, radiating, subparallel, sheaf- or spray-like) aggregates up to 2 cm consisting of fibers up to 1.4 cm long and 0.01 mm thick. Rarely, aggregates of acicular crystals up to 1 cm long and 0.03 mm thick, elongate along [001], with a tetragonal or octagonal cross-section, and fibrous pseudomorphs after eudidymite are observed. Individual crystals of niveolanite are colorless and transparent. Aggregates are snow-white to pearl-white, with a silky luster. The density calculated for the empirical formula with 1.66 H 2 O pfu is 2.06, whereas that for the less hydrous variety (1 H 2 O pfu ) is 1.82 g/cm 3 . Niveolanite is optically uniaxial positive, ω 1.469(1), e 1.502(1). The IR spectrum is unique. The averaged chemical composition (Na, K and Ca were determined by electron microprobe, Be by ICP–OES, [CO 2 + H 2 O] from loss on ignition, CO 2 by selective absorption) is: Na 2 O 19.81, K 2 O 0.07, CaO 3.88, BeO 16.65, CO 2 29.81, H 2 O 26.93, total 97.15 wt.%. The empirical formula calculated for 1 C apfu is: (Na 0.94 Ca 0.10 ) ∑1.04 Be 0.98 (CO 3 ) 1.00 (OH) 1.10 ·1.66H 2 O. In moist air, niveolanite strongly absorbs molecular water; the process of its hydration–dehydration is easily reversible. Niveolanite is tetragonal, P 4/ mcc , a 13.1304(19), c 5.4189(11) A, V 934.3(3) A 3 , Z = 8. The strongest ten lines of the X-ray powder diagram [ d in A ( I )( hkl )] are: 13.01(100) (100), 9.20(62)(110), 4.343(27)(300), 3.611(34)(320), 3.269(22)(311), 3.256(95)(400), 2.693(44)(002), 2.605(37)(430,500), 2.489(60)(202), and 2.076(32)(620). The crystal structure was solved using a single crystal and synchrotron radiation, R = 0.0358. Niveolanite represents a new structure-type. Its structure includes isolated, infinite chains of BeO 2 (OH) 2 tetrahedra linked via common OH groups; two other vertices of each Be tetrahedron are shared with (CO 3 ) groups, and Na cations occupy seven-fold polyhedra [NaO 6 (H 2 O)] forming columns. Chains of Be tetrahedra and columns of Na polyhedra are aligned along the c axis, just as broad channels in which H 2 O molecules are located. The structural formula is: {(Na 0.9 Ca 0.1 )[(H 2 O) 0.9 (OH) 0.1 ]}{Be(OH)} (CO 3 )·0–1H 2 O. The idealized formula is: NaBe(CO 3 )(OH)·1–2H 2 O. The mineral was named from Latin niveus , snow-white, and lana , wool, alluding to the visual similarity of its aggregates to snow-white, fluffy flocks of wool. The cotype specimens are deposited in the Fersman Mineralogical Museum of Russian Academy of Sciences, Moscow, and the Canadian Museum of Nature, Ottawa.