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Friisite, Pb.sub.8Al.sub.3Si.sub.8O.sub.27Cl.sub.3, a new mineral with a polysomatic relation to jagoite, from Långban, Sweden
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Friisite, Pb.sub.8Al.sub.3Si.sub.8O.sub.27Cl.sub.3, a new mineral with a polysomatic relation to jagoite, from Långban, Sweden
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Journal Article
Friisite, Pb.sub.8Al.sub.3Si.sub.8O.sub.27Cl.sub.3, a new mineral with a polysomatic relation to jagoite, from Långban, Sweden
2026
Overview
Friisite, ideally Pb.sub.8 Al.sub.3 Si.sub.8 O.sub.27 Cl.sub.3, is a new mineral discovered in a museum sample from the Långban mine in Värmland, Sweden. It occurs as subhedral, flaky grains up to 150 µm in size, forming aggregates within a medium-grained skarn matrix and contiguous to jagoite. Both are associated with melanotekite, aegirine-augite, albite, baryte, fluorapophyllite-K, margarosanite, alamosite, native lead, a serpentine group mineral, and a wickenburgite-like mineral. Friisite is white to colorless with a white streak and sub-adamantine luster. The mineral is transparent and does not fluoresce under UV light. It is brittle, with an uneven fracture and perfect cleavage on 001. Mohs hardness is 4-5 (by analogy with jagoite). The calculated density is 5.54(1) g cm.sup.-3 . Optically, friisite is non-pleochroic and uniaxial (-). Point analyses by means of an electron microprobe using wavelength-dispersive spectroscopy resulted in an empirical formula (based on 30 O+Cl): (Pb7.89Na0.11Ca0.08)â=8.08(Al2.19Si0.31Fe0.203+Zn0.13Mn0.112+)â=2.94Si8O27.02Cl2.98. Friisite is hexagonal, P6-2c (#190), with unit-cell parameters a=8.5955(1) Ã, c=23.4092(2) Ã, and V=1497.82(4) Ã.sup.3 for Z=2. The eight strongest powder X-ray diffraction lines are [d, à (I.sub.rel) (hkl)]: 5.848 (31) (004), 5.375 (20) (103), 4.040 (96) (11-2, 112), 3.680 (40) (201), 3.463 (100) (114), 2.886 (21) (116), 2.795 (20) (21-1), and 2.4828 (35) (300). Friiste is a phyllosilicate and forms a polysomatic series with jagoite characterized by a layer sequence of SiO.sub.4 tetrahedra (T) and metal octahedra (O) between double layers (*) corresponding to *TOT*, whereas jagoite is described as *TOTOT*. Friisite forms from transformation of melanotekite or barysilite in the presence of albite and a Cl-enriched fluid at relatively high aSiO2. The mineral (IMA2024-047) is named in honor of Danish mineralogist Henrik Friis (b. 1977), professor at the Natural History Museum, University of Oslo, Norway.
Publisher
Copernicus GmbH
Subject
