Hard, blue-white metal. Soluble in HCl and H2SO4 but not
HNO3, H3PO4 or HClO4 due to formation of protective layer. Resists
oxidation in air. Main use in alloys, chrome plating, and metal ceramics.
Diagnostic tests:
Chromium gives a borax bead test in the reducing flame a color which is yellow
to red (hot) and yellowish green (cold). Under the reducing flame the bead
color is a fine emerald green, hot and cold.
Chromium gives a Na2(NH4)(PO4) bead a
dirty green color (hot) and a fine green color (cold).
In solution, the addition of NH4OH produces a green precipitate
of Cr(OH)3. Note: chromium's name is in reference to the
various colors a solution will have depending on the oxidation state Cr2+
(yellow), Cr3+ (green), or Cr6+ (orange).
References
Emsley, J., 1991; THE ELEMENTS : Sec. Ed.,
Clarendon Press, Oxford, 251 p.
(* - Mineral Name Is Not IMA Approved)
(! - New Dana classification added or changed from Danas New Mineralogy)
(? - IMA Discredited Mineral Species Name)
There are 103 minerals with Cr in the Mineralogy Database.