Instalment of the margarosanite group, and data on walstromite–margarosanite solid solutions from the Jakobsberg Mn–Fe deposit, Värmland, Sweden

Abstract The margarosanite group (now officially confirmed by IMA-CNMNC) consists of triclinic Ca-(Ba, Pb) cyclosilicates with three-membered [Si 3 O 9 ] 6– rings (3R), the general formula AB 2 Si , where A = Pb, Ba and Ca B Ca. closest-packed arrangement atoms parallel to (101) hosts cations in interstitial sites alternating layers. 3R layer has three independent each ring. Divalent occupy sites: occupies two nonequivalent sites, 1 (8-fold coordinated), (6-fold coordinated). (= 3) is occupied Pb 2+ (or ) 6+4 coordination, or 6+1 when Ca; this third site occurs within 3R-layer a peripheral position. Three minerals belong group: (ideally PbCa ), walstromite (BaCa breyite (CaCa ). So far, no solid solutions involving have been described. Therefore, root names depend on composition only. Isomorphic replacement at noted. We here report data skarn sample from Jakobsberg Mn–Fe oxide deposit, Värmland, Sweden, representing intermediate compositions walstromite–margarosanite binary, range ca. 50–70% mol.% BaCa . Pb-rich associated closely celsian, phlogopite, andradite, vesuvianite, diopside nasonite. crystal-structure refinement ( R 4.8%) structure type, showed that (Ba, split into positions separated 0.39 Å, found slightly more 3R-layers.