Hemimorphite
Hemimorphite is a mineral that occurs as a secondary mineral in the oxidation zones of zinc deposits, often taking on crust-like or botryoidal forms. Because analytical techniques were insufficient in the past, it was called "calamine" (particularly in the United States).
Hemimorphite often occurs as botryoidal aggregates
Basic Information
| English Name | Hemimorphite |
|---|---|
| Japanese Name | Ikyokuko (異極鉱) |
| Chemical Formula | Zn4[(OH)2|Si2O7]・H2O |
| Crystal System | Orthorhombic |
| Hardness | 4.5–5 |
| Specific Gravity | 3.4 |
| Transparency | — |
Characteristics & Variations
- Calamine: A name used to refer to a mixture of white minerals, including not only hemimorphite but also smithsonite (ZnCO3), hydrozincite, and others.
- Origin of Japanese Name: Named "Ikyokuko" (meaning "different-pole mineral") due to its hemimorphic crystal structure.
- Origin of English Name: Derived from "hemi" (half) and "morphe" (form), referring to its hemimorphic crystal habit in botryoidal aggregates.
- Color: Originally white, but becomes blue to yellowish-greenish blue when it contains Fe or Cu. Blue varieties are common.
- Banding: Can sometimes exhibit banding in association with smithsonite; the deeper blue portions are hemimorphite.
Trade Names, Treatments & Similar Stones
Trade Names: "Zinc Turquoise" (due to its zinc content and turquoise-like blue color), "Zinc Paraiba" (a name coined to capitalize on the popularity of blue Paraiba tourmaline).
Treatments: Dyeing (for paler stones) and resin impregnation (for porous stones) are sometimes performed.
Similar Stones: Smithsonite. Blue varieties are difficult to distinguish with the naked eye, but generally, hemimorphite has a higher refractive index and appears more lustrous, while smithsonite is heavier due to its higher specific gravity. When exposed to dilute HCl, smithsonite effervesces and dissolves, whereas hemimorphite decomposes without effervescence.
Note: Appearance can vary significantly depending on whether the stone has been dyed or impregnated. Please exercise caution regarding identification and the use of chemicals during cleaning.