Smithsonite and hemimorphite are two very different minerals. Smithsonite is a carbonate mineral and a member of the trigonal crystal system, while hemimorphite is a silicate mineral and orthorhombic. They also have noticeable differences in specific gravity and cleavage.
Even with these differences, the two minerals were confused with one another and identified by the name “calamine” until the mid- to late-1800s. An important contributor to this confusion is the fact that they were both often microcrystalline, translucent, and often intergrown with one another in a botryoidal crystal habit. As a result they were long thought to be the same mineral.
Investigators who know a few basic properties of these minerals and have the needed tools can easily identify them in monomineralic specimens. Identifying the mixture is more challenging. Use these properties:
- Smithsonite will effervesce under a drop of cold, dilute hydrochloric acid, but hemimorphite will not.
- Hemimorphite has a lower specific gravity (3.4 to 3.5) than smithsonite (4.3 to 4.5).
- Hemimorphite has perfect cleavage in one direction, but smithsonite has perfect cleavage in two directions that meet to form rhombic angles.
- Mixtures of these minerals will have an intermediate specific gravity and will react with cold, dilute hydrochloric acid.
| Physical Properties of Smithsonite | |
| Chemical Classification | Carbonate |
| Color | Usually brown or gray, but may be colorless, white, yellow, green, blue or pink. The colors can be spectacular, and that makes smithsonite popular with people who collect mineral specimens and gems. |
| Streak | White |
| Luster | Vitreous to pearly |
| Diaphaneity | Translucent |
| Cleavage | Perfect rhombohedral cleavage. Uneven to conchoidal fracture. |
| Mohs Hardness | 4 to 4 1/2 |
| Specific Gravity | 4.3 to 4.5 |
| Diagnostic Properties | Effervesces with cold, dilute hydrochloric acid (5% to 10%), high specific gravity, low hardness. Cleavage is similar to calcite. Botryoidal habit. |
| Chemical Composition | ZnCO3 |
| Crystal System | Trigonal |
| Uses | An ore of zinc. Specimens are popular with mineral collectors. Sometimes cut into gems for collectors. |