Formula: Ni2(CO3)(OH)2.H2O
Hydrated carbonate containing hydroxyl, nickel-bearing mineral
Crystal System: Orthorhombic
Specific gravity: 3.41 measured, 3.346 calculated
Hardness: 4
Colour: Green, bright green
Solubility: Dissolves slowly in cold 1:1 hydrochloric acid; at 100oC it dissolves rapidly, with visible evolution of CO2 bubbles
Common impurities: Mg

Metamorphic environments
Hydrothermal environments


At the type locality, the Otway Ni deposit, Nullagine, East Pilbara Shire, Western Australia, otwayite was found in three samples. The deposit is an ultramafic body cut by numerous shears that contain an unusual mineral assemblage including apatite, chlorite, magnesite, gaspéite, pecoraite, millerite and polydymite.
Otwayite has so far been found only in narrow veinlets between 0.5 and 1 mm in width. The veinlets appear to represent late-stage fracture filling, and transect nickel-bearing serpentine, millerite, polydymite and apatite. Associated with the otwayite in the veinlets are magnesite, gaspéite and pecoraite. The otwayite has a pronounced fibrous habit, with the fibres usually arranged in rosette-like aggregates (AM 62.999-1002). Other associated minerals include paraotwayite and chrysotile (Mindat).

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