Cobaltite or cobalt glance is a very uncommon mineral that
forms in sulphur-rich veins when the metals cobalt and
arsenic join to form a sulphide. The very rarity of cobaltite
crystalsmakes them much sought after by collectors.
Cobaltite forms cubic crystals that look very similar
toiron pyrite, although the actual structure is
slightly different. Fortunately cobaltite is easily
distinguished from pyrite by its colour. Pyrite is
brassy yellow while cobaltite is silvery white.
However, it is much harder to tell cobaltite from
one of the other cobalt ores, skutterudite, which
is also white and forms cubic crystals.
Sometimes, when cobaltite has been exposed to
the air, it will become covered with a bright pink or
purplecrust of other minerals such as erythrite. This
colourful crust is called 'cobalt bloom' and is a strong sign
of the presence of cobaltite or skutterudite. Cobaltite is
one of the important ores of cobalt.