Никельді қабатты силикаттар: Гарниерит минералының құрамы мен қасиеттері

Nickel layer silicate

Garnierite is a general name for a green nickel ore which is found in pockets and veins within weathered and serpentinized ultramafic rocks. It forms by lateritic weathering of ultramafic rocks and occurs in many nickel laterite deposits in the world. It is an important nickel ore, having a large weight percent NiO. As garnierite is not a valid mineral name according to the Commission on New Minerals, Nomenclature and Classification (CNMNC), no definite composition or formula has been universally adopted. Some of the proposed compositions are all hydrous Ni Mg silicates, a general name for the Ni Mg hydrosilicates which usually occur as an intimate mixture and commonly includes two or more of the following minerals: serpentine, talc, sepiolite, smectite, or chlorite, and Ni Mg silicates, with or without alumina, that have x ray diffraction patterns typical of serpentine, talc, sepiolite, chlorite, vermiculite or some mixture of them all.

Various studies have examined the composition of garnierite. In 1964, a study was done on the composition of a talc like garnierite and found the composition to be close to the compositions of stevensite and sepiolite, but with partial replacement of the Mg content by Ni. In 1973, another study found that chemical analysis of garnierite samples yields non stoichiometric formulae that can be reduced to formulas like those of talc and serpentine. The authors suggested a talc monohydrate formula of |(Mg,Ni)3Si4O10(OH)2·H2O for the talc like garnierite. In 2011, the most recent study performed used Extended X ray Absorption Fine Structure (EXAFS) analysis to determine the composition of their garnierite samples. It found that garnierite has an almost complete solid solution between Ni sepiolite and falcondoite, with samples analyzed showing between 3 and 77 percent falcondoite composition.

Garnierite is generally a fine grained mineral with poor crystalline structure. The fact that Ni readily substitutes for Mg in garnierite explains why as NiO content goes up, MgO content goes down. The nickel in garnierite is not evenly distributed throughout the structure, but is concentrated in small zones of nickel surrounded by magnesium zones. The main difference between the serpentine like and talc like variants of garnierite is the spacing between layers in the structure, seen in X ray powder diffraction studies. The serpentine like variants have 7 Å basal spacings while the talc like variants have a basal spacing of 10 Å. Some species of garnierite stick to the tongue and dissolve readily in water or even on the tongue. X ray diffraction of samples from that mine show that garnierite veins include sepiolite falcondoite and quartz (chrysoprase, a green variety of quartz with a nickel content of less than 2 weight %). Breccias found in faults at the Falcondo mine contain garnierite clasts cemented together by a secondary deposition of garnierite, which is evidence of syn tectonic deposition of garnierite. In the garnierite deposits near Riddle, Oregon, garnierite is found as a weathering product of the underlying peridotite, with the garnierite layer between thick.

Jules Garnier, a French geologist, published his work on the geology of New Caledonia in 1867, announcing the discovery of nickel there. Garnierite was named for Jules Garnier in a paper by Archibald Liversidge in 1874. When Liversidge sent a copy of his paper to Garnier, Garnier replied that the new mineral noumeite being described in the paper sounded very much like a mineral he had described in his 1869 paper. Liversidge decided to name the new mineral garnierite in honor of Garnier and gave the name noumeaite to a second mineral found in the same general area in New Caledonia.