| Reference Type | Journal (article/letter/editorial) |
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| Title | Woodallite, a new chromium analogue of iowaite from the Mount Keith nickel deposit, Western Australia |
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| Journal | Mineralogical Magazine |
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| Authors | Grguric, B. A. | Author |
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| Madsen, I. C. | Author |
| Pring, A. | Author |
| Year | 2001 (June) | Volume | 65 |
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| Issue | 3 |
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| Publisher | Mineralogical Society |
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| DOI | doi:10.1180/002646101300119501Search in ResearchGate |
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| Generate Citation Formats |
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| Mindat Ref. ID | 243275 | Long-form Identifier | mindat:1:5:243275:9 |
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| GUID | 0 |
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| Full Reference | Grguric, B. A., Madsen, I. C., Pring, A. (2001) Woodallite, a new chromium analogue of iowaite from the Mount Keith nickel deposit, Western Australia. Mineralogical Magazine, 65 (3) 427-435 doi:10.1180/002646101300119501 |
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| Plain Text | Grguric, B. A., Madsen, I. C., Pring, A. (2001) Woodallite, a new chromium analogue of iowaite from the Mount Keith nickel deposit, Western Australia. Mineralogical Magazine, 65 (3) 427-435 doi:10.1180/002646101300119501 |
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| Abstract/Notes | AbstractWoodallite is a new Cr-rich member of the hydrotalcite group from the large, low-grade Mount Keith nickel deposit, in the northeastern Goldfields district of Western Australia. Woodallite occurs as whorls and clusters of minute platelets up to 6 mm across in lizardite+brucite-altered dunite. Individual platelets are typically 10–100 µm in maximum dimension and are often curved. Associated minerals include chromite, lizardite, iowaite, pentlandite, magnetite, tochilinite and brucite. Electron microprobe analysis gave: Mg 25.90 wt.%; Cr 10.81; Fe 4.86; Al 0.68; Cl 9.89; S 0.03; Si 0.01; Ni 0.01; Na 0.01, yielding (after correction for loss of volatiles) an empirical formula of Mg6.19(Cr1.21Fe0.51Al0.15)∑1.87(OH)16[Cl1.62(CO3)0.17(SO4)0.01]·4H2O, by analogy with the hydrotalcite group. The simplified formula is Mg6Cr2(OH)16Cl2·4H2O. Combined thermogravimetric analysis and mass spectroscopy showed a two-stage weight loss of 12.7% and 27.3% occurring over the ranges 25–300°C and 300–660°C, respectively. The first weight loss is attributed to loss of interlayer water, chlorine-bearing species (e.g. HCl) and some CO2, the second to loss of hydroxide water, remaining CO2 and Cl species. The mineral is deep magenta to purple in colour, transparent, with a resinous to waxy lustre, and a perfect basal {0001} cleavage. Woodallite has a Mohs hardness of 1.5–2, and a pale-pink to white streak. The strongest lines in the X-ray powder pattern are [dobs (Iobs) (hkl)] 8.037 (100) (003); 4.021 (48) (006); 2.679 (1) (009); 2.624 (3) (012); 2.349 (5) (015); 2.007 (6) (0,0,12); 1.698 (2) (0,1,11); 1.524 (2) (21̄3). These lines were indexed on a hexagonal cell with a = 3.103(2), c = 24.111(24)Å, V = 201.14 Å3 and Z = 3/8. The new mineral is isostructural with the hydrotalcite group and has space group R3̄m. The measured density is 2.062 gm/cm3. Woodallite is uniaxial negative with ω = 1.555 and ε = 1.535 (white light); pleochroism is distinct from violet to pinkish lilac. Woodallite forms as a result of hydrothermal alteration of primary magmatic chromite by Clrich solutions at temperatures <320°C. Relict chromite fragments are frequently present in the whorls, and associated magnetite is altered extensively to iowaite. The mineral is named after Roy Woodall, eminent Australian industry geologist. |
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