Cobalt it reacts slowly with mineral acids, and very slowly with moist, but not with dry, air. Common oxidation states of cobalt include +2 and +3, although compounds with oxidation states ranging from −3 to +5 are also known. A common oxidation state for simple compounds is +2 (cobalt(II)). These salts form the pink-colored metal aquo complex [Co(HO)] in water. Addition of chloride gives the intensely blue . In a borax bead flame test, cobalt shows deep blue in both oxidizing and reducing flames. Several oxides of cobalt are known. Green cobalt(II) oxide (CoO) has rocksalt structure. It is readily oxidized
Cobalt sulfide Cobalt sulfide Cobalt sulfide is the name for chemical compounds with a formula CoS. Well-characterized species include minerals with the formula CoS, CoS, CoS, and CoS. In general, the sulfides of cobalt are black, semiconducting, insoluble in water, and nonstoichiometric. Cobalt sulfides occur widely as minerals, comprising major sources of all cobalt compounds. Binary cobalt sulfide minerals include the cattierite (CoS) and linnaeite (CoS). CoS (see image in table) is isostructural with iron pyrite, featuring disulfide groups, i.e. CoS. Linnaeite, also rare, adopts the spinel motif. The CoS compound is known as a very rare cobaltpentlandite (the Co analogue of