Hemimorphite is a zinc silicate with one of the loveliest sky blues in the mineral world. Its tongue-twister name refers to its crystals, which have different shapes at each end, a quirk mineralogists call hemimorphism. The gem material jewellers love is the botryoidal form, rounded bubbly crusts in pale to electric blue, often streaked with white. Top sources include the Wenshan mine in China, the Democratic Republic of the Congo and Mexico. Historically it was mined as a zinc ore under the old name calamine.
Hemimorphite is soft, around 4.5 to 5 on the Mohs scale, and brittle with it, so it is strictly a special-occasion stone. Think pendants and earrings rather than rings, and store it apart from harder gems. It is cut as cabochons and beads that show off the blue banding. Keep it away from acids, ultrasonic cleaners and knocks, and wipe it with a soft, barely damp cloth. Its colour rivals fine turquoise, which is exactly why collectors put up with the extra care.
All share that soft sky-blue palette, though each is a completely different mineral.
