Hawthorneite, Ba[Ti3Cr4Fe4Mg]O19: a new metasomatic magnetoplumbite-type mineral from the upper mantle
Article
Haggerty, SE, Grey, IE, Madsen, IC et al. (1989). Hawthorneite, Ba[Ti3Cr4Fe4Mg]O19: a new metasomatic magnetoplumbite-type mineral from the upper mantle
. AMERICAN MINERALOGIST, 74(5-6), 668-675.
Haggerty, SE, Grey, IE, Madsen, IC et al. (1989). Hawthorneite, Ba[Ti3Cr4Fe4Mg]O19: a new metasomatic magnetoplumbite-type mineral from the upper mantle
. AMERICAN MINERALOGIST, 74(5-6), 668-675.
A new opaque mineral oxide is described from a veined, metasomatized, harzburgitic xenolith from a diamondiferous kimberlite pipe in Kimberley, South Africa. The new mineral, hawthorneite (~100 μm in maximum dimension), is in intimate association with lindsleyite (Ba,Sr)(Ti,Cr...)21O38, a member of the crichtonite group, accessory niobian chromian rutile, and magnesian chromian ilmenite in host-replacement-textured magnesian chromite. Hawthorneite is isostructural with magnetoplumbite Pb(Fe,Mn)12O19 and barium ferrite (BaFe12O19). A typical average composition is (Ba0.85K0.12)[Cr4.68Ti3.02Fe2+2.02Fe3+1.47Mg0.80 Mn0.02Nb0.01]O19 or ideally Ba[Cr4Ti3Fe4Mg]Σ12O19. The space group is P63/mmc with Z = 2, and the strongest reflections are [dcalc(Å), Icalc, hkl] 2.616(100)(114), 2.765(85)(017), and 2.414(49)(023). Hexagonal unit-cell parameters are a = 5.871(2) Å and c = 23.06(2) Å, and the structure comprises alternating spinel-type slabs and perovskite-type layers. The calculated density is 5.02 g/cm3. Hawthorneite is pale gray in reflected light, is nonpleochroic with weak to moderate bireflectance, and has weak to moderate rotation tints in browns and grays. Quantitative spectral reflectance measurements for Ro and R′e in air and oil immersion, respectively, are for 470 nm 18.3, 17.1 and 6.02, 5.25%; for 546 nm 17.5, 16.4 and 5.58, 4.88%; for 589 nm 17.3, 16.3 and 5.41, 4.75%; and for 650 nm 17.05, 16.0 and 5.34, 4.68%. VHN100 = 801, with a range of five indentations = 772-835. -from Authors
