[3][4][5] In the first step, erbium(III) oxide is heated with ammonium chloride to produce the ammonium salt of the pentachloride: In the second step, the ammonium chloride salt is converted to the trichloride by heating in a vacuum at 350-400 °C: Erbium(III) chloride forms crystals of the AlCl3 type, with monoclinic crystals and the point group C2/m.

[2] Erbium(III) chloride hexahydrate also forms monoclinic crystals with the point group of P2/n (P2/c) - C42h.

In this compound, erbium is octa-coordinated to form [Er(H2O)6Cl2]+ ions with the isolated Cl− completing the structure.

[6] Erbium(III) chloride solutions show a negative nonlinear absorption effect.

[7][clarification needed] The use of erbium(III) chloride as a catalyst has been demonstrated in the acylation of alcohols and phenols[8] and in an amine functionalisation of furfural.