A new occurrence of samuelsonite in the Buranga Pegmatite, Rwanda

• Main Authors: A.-M. Fransolet, O. von Knorring, F. Fontan
• Format: Article
• Language: English
• Published: Geological Society of Finland 1992-06-01
• Series: Bulletin of the Geological Society of Finland
• Subjects: minerals; phosphates; samuelsonite; chemical composition; infrared spectra; crystal structure; pegmatite; Buranga; Rwanda
• Online Access: http://www.geologinenseura.fi/bulletin/Volume64/sgs_bt_064_1_pages_013_021.pdf

A new occurrence of the rare mineral species, samuelsonite, is reported from the Buranga pegmatite, Rwanda, in close association with gatumbaite and burangaite, as aggregates of bladed crystals imbedded in trolleite and in bertossaite. Its crystallographic properties, determined both by the rotation and Wassenberg techniques and by the powder method, are: a= 18.621(3), b = 6.842(1), c = 14.066(2)Å, ß = 112°30'(1’), C2/m, Z = 2.Gmeas = 3.24(5) and Gcalc =3.22. A wet chemical analysis gives: 43.79 P2O5, 6.18 Al2O3, 0.07 Fe2O3, 7.92 FeO, 8.91 MnO, 0.07 MgO, 28.41 CaO, 2.31 BaO, 0.43 Li2O, 0.35 Na2O, 1.85 H2O+, total 100,29%. Because of some structural similarities with the apatite structure, a few assigments of the infrared absorption bands are tentatively proposed. A discussion on the crystal chemistry shows that Li resides in the octahedral M sites, whereas Na is sequestred with the excess of Mn and Ca in the X sites of the structure.