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Formula: Ni2+1-xCo3+x(OH)2-x(SO4)x.nH2O [x ≤ ⅓; n ≤ (1-x)]
Hydroxide, nickel- and cobalt-
bearing mineral
Crystal System: Trigonal
Specific gravity: 2.67 measured, 2.69 calculated
Colour: Green
Solubility: Insoluble in water but slowly soluble in cold dilute hydrochloric acid without any visible reaction
Environments
Jamborite was redefined in 2014.
Localities
There are four co-type localities, Ca' dei Ladri, Gaggio Montano, Metropolitan City of Bologna; Monteacuto Ragazza,
Grizzana Morandi, Metropolitan City of Bologna; Sasso delle Lucine, Castelluccio di Moscheda, Montese, Modena
Province; Rio Vesale, Vesale, Sestola, Modena Province; all at Emilia-Romagna, Italy.
At the type localities jamborite was found associated with
millerite in small cavities in
ophiolitic rocks. It occurs as a green coating on the walls of
cavities lined by calcite,
dolomite and quartz crystals. The
coatings seem to consist of sheaves of transparent, single crystals
pseudomorphous after
millerite. The interior zones of some "crystals" contain unaltered
millerite. All gradations occur between pure
millerite and jamborite.
Jamborite is included within quartz and
calcite in some places. Each aggregate of jamborite consists of
microcrystalline individuals, either acicular or lamellar, and of crypto-crystalline or even isotropic patches that
chiefly occur in the centre of an aggregate. These facts, together with the occurrence of
pseudomorphs of jamborite after
millerite, indicate that jamborite did not form by simple
weathering of millerite but by gradual, probably low-temperature,
hydrothermal alteration.
Millerite was formed in an early hydrothermal
stage under reducing conditions. Later, more oxidising alteration converted
millerite into nickel hydroxide. The
millerite underwent hydrolysis and then partial oxidation. The
hydrolysis led to a partial replacement of S by OH, yielding an isotropic material whose remnants still can be
seen within the crystalline jamborite. The more crystalline jamborite could have been produced by a
slow oxidation inward from the surface, gradually producing an ordered crystalline structure
(AM 58.835-839).
At the Nakauri mine, Shinshiro city, Aichi Prefecture, Japan, jamborite occurs in
serpentinites, associated with
gaspéite, glaukosphaerite
and mcguinnessite
(HOM).
At Halls Gap, Lincoln county, Kentucky, USA, another occurrence of what may be jamborite has been found. The
pale green mineral occurs as an alteration product of capillary millerite in
quartz-lined geodes
(AM 58.835-839).
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