This is a sample of chromium (III) chloride, hexahydrate. This chemical exists as three isomers, being

• pale green [CrCl(H₂O)₅]Cl₂ · H₂O
• dark green [CrCl₂(H₂O)₄]Cl · 2H₂O
• violet [CrCl₃(H₂O)₃] · 3H₂O

The isomers differ in the ligands, coordinated to the chromium (III) core. The sample, shown here, is the second one, with two chloride ligands attached to the chromium ion. If this compound is dissolved in water, then a bright green solution is obtained. With silver nitrate solution, only one third of the chloride is precipitated, the rest is strongly coordinated to the chromium and is not easily released. Such a solution contains the bright green cation CrCl₂(H₂O)₄⁺, instead of the violet/bluish hexaaqua ion of chromium (III).

All three isomers exist, but the commercial preparation of chromium (III) chloride hexahydrate is the dark green isomer.