1984/06/01 by Pete J. Dunn, Donald R. Peacor
paper · doi:10.1180/minmag.1984.048.347.13
crossref issued 1984/06/01 · crossref published 1984/06/01 · crossref published-print 1984/06/01 · crossref created 2006/12/09 · crossref published-online 2018/07/05 · crossref deposited 2021/02/05 · crossref indexed 2026/07/30
Abstract Nelenite, (Mn,Fe) 16 si 12 O 30 (OH) 14 [ O 6 (OH) 3 ], is a polymorph of schallerite and a member of the friedelite group. X-ray diffraction patterns can be indexed on a supercell with a = 13.418(5) and c = 85.48(8)A, space group R m, but by analogy with TEM results on mcGillite and friedelite, the structure is based on a one-layer monoclinic cell with a = 23.240, b = 13.418, c = 7.382 Å, β = 105.21°, and space group C 2/ m . Chemical analysis yields SiO 2 31.12, FeO 17.12, MgO 0.12, ZnO 3.63, MnO 29.22, As 2 O 3 12.46, H 2 O 6.42, sum = 100.09%. Analysis of a number of samples indicates that Fe substitutes for Mn up to 5.8 of the 16 octahedrally coordinated cations, but that the Si: As ratio is constant. The strongest lines in the X-ray powder diffraction pattern ( d, I/Io ) are: 2.552, 100 ; 2.878, 70 ; 1.677, 60 ; 3.55, 60 ; 1.723, 50 . Nelenite is brown in colour with a vitreous luster and perfect 0001 cleavage, which easily distinguishes it from schallerite. The Mohs' hardness is approximately 5. The density is 3.45 g/cm 3 (calc.) and 3.46 g/cm 3 (obs.). Nelenite is uniaxial negative with ɛ = 1.700 and ω = 1.718 (both ± 0.004). Nelenite was formerly known as ferroschallerite , which is a misnomer. It was found in the Franklin Mine, Franklin, Sussex County, New Jersey, in the 1920s. It occurs in several parageneses, associated with actinolite, tirodite, albite, garnet, feldspars, and several members of the stilpnomelane group in coarse-grained assemblages with pegmatitic texture and a breccia likely derived from this rock. Nelenite is named in honour of Joseph A. Nelen, chemist at the Smithsonian Institution.