• journal_title：The Canadian Mineralogist
• Contributor：Anthony R. Kampf ; Andrew C. Roberts ; Katherine E. Venance ; Gail E. Dunning ; Robert E. Walstrom
• Publisher：Mineralogical Association of Canada
• Date：2011-
• Format：text/html
• Language：en
• Identifier：10.3749/canmin.49.2.587
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：49
• issue：2
• firstpage：587
• section：Articles

Ferroericssonite, ideally BaFe²⁺₂Fe³⁺(Si₂O₇)O(OH), is a new mineral species found at both the Esquire #7 and #8 claims, situated along Big Creek in eastern Fresno County, and also at Trumbull Peak in Mariposa County, California, U.S.A. The mineral is the Fe²⁺ analogue of ericssonite and is named accordingly. Ferroericssonite crystallized very late in a sequence of minerals resulting from fluids interacting with a quartz−sanbornite vein along its margin with the country rock. It is closely associated with anandite, bazirite, celsian, devitoite, quartz and titantaramellite. The crystals occur in dark reddish brown foliated masses of irregular, undulating striated blades up to several mm in length, flattened on {100} and elongate and striated parallel to [001]. The mineral is transparent and has a brown streak, a vitreous luster, a Mohs hardness of approximately 4½, and two cleavages: {100} perfect and {011} good. It is brittle with an irregular fracture. The calculated densities are 4.445 and 4.413 g/cm³ on the basis of the empirical formulas for Esquire #7 and Esquire #8 material, respectively. It is optically biaxial (+), α 1.827(3), β 1.845(3), γ 1.920(6) (white light); 2V_meas = 63(2)°; 2V_calc = 63.0°; parallel dispersion, r < v; orientation: X = b, Y ≈ c, Z ≈ a; pleochroic: brown, Z > X > Y. Electron-microprobe analyses of Esquire #7 and Esquire #8 material provided: BaO 30.11, 29.76, MgO 0.21, 0.10, MnO 1.19, 0.79, FeO 26.01, 26.24, Fe₂O₃ 15.30, 15.35, Al₂O₃ 0.02, 0.04, SiO₂ 22.89, 23.34, F 0.09, 0.05, Cl 1.29, 0.88, H₂O 1.33, 1.42, F + Cl≡ O −0.33, −0.22, total 98.11, 97.75 wt%, with FeO and Fe₂O₃ assignments and H₂O based on the structure. The empirical formulas for Esquire #7 and Esquire #8 material, based on Mg + Fe + Mn + Si = 5 apfu, are Ba_1.02(Fe²⁺_1.89Mn²⁺_0.09Mg_0.03)_∑2.01Fe³⁺_1.00(Si_1.99O₇)O[(OH)_0.77O_0.02Cl_0.19F_0.02]_∑1 and Ba_1.01(Fe²⁺_1.90Mn²⁺_0.06 Mg_0.01)_∑1.97Fe³⁺_1.00(Si_2.02O₇)O[(OH)_0.82O_0.04Cl_0.13F_0.01]_∑1, respectively. Ferroericssonite is monoclinic, C2/m, a 20.3459(10), b 7.0119(3), c 5.3879(4) Å, β 94.874(7)°, V 765.89(7) ų and Z = 4. The strongest five lines in the X-ray powder-diffraction pattern [d_obs in Å(I)(hkl)] are: 3.708(42)(3̅11), 3.506(81)(311, 510, 020), 2.880(42)(420), 2.788(100)(221) and 2.663(83)( 2̅02, 710). The crystal-structure determination (R₁ = 3.56% for 885 F_o > 4σF) shows the mineral to be a heterophyllosilicate with a Fe²⁺ trioctahedral (O) sheet flanked on either side by heterophyllosilicate (H) layers, forming a HOH composite sheet. The heterophyllosilicate layers are composed of Si₂O₇ groups linked by Fe³⁺ square pyramids in a configuration referred to as a TS (Ti silicate) block, although five-coordinated Fe³⁺ takes the place of Ti⁴⁺. The region between the composite sheets is occupied by Ba²⁺. Ferroericssonite is a member of the lamprophyllite group.