Hemimorphite: Gemstone Information
Hemimorphite is Zn4Si2O7(OH)2H2O and is found either as orthorhombic thin tabular crystals with double terminations, showing hemimorphism, or more commonly in masses. Attractive translucent light blue cabochons have been fashioned from Mexican specimens and some transparent faceted stones are known. The hardness is 4.5–5 and there is one direction of perfect cleavage. The SG is 3.4–3.5 and the RI for the alpha, beta and gamma rays is 1.614, 1.617 and 1.636, biaxial positive with a birefringence of 0.021. Hemimorphite occurs as a secondary mineral in the oxidized zone of zinc-bearing mineral deposits. Apart from the facetable crystals the masses, often sheaf- or fan-like, have their own attraction. The main source is Santa Eulalia, Chihuahua, Mexico.