Hemimorphite
Hemimorphite is a zinc silicate hydroxide mineral crystallizing in the orthorhombic system and named for its hemimorphic crystals, which develop different faces at opposite ends of the same crystal axis. It typically forms in the oxidized zones of zinc ore deposits, often intergrown with or resembling smithsonite, another secondary zinc mineral. Its delicate, fan-shaped crystal clusters and pastel blue to white coloring make it a favorite among collectors of secondary zinc minerals.
Hemimorphite properties at a glance
| Type | Minerals |
|---|---|
| Chemical formula | Zn4Si2O7(OH)2·H2O |
| Mohs hardness | 4.5–5 |
| Crystal system | Orthorhombic |
| Luster | Vitreous, silky when fibrous |
| Streak | White |
| Cleavage | Perfect on {110} |
| Fracture | Uneven to conchoidal |
| Specific gravity | 3.4–3.5 |
| Transparency | Transparent to translucent |
| Common colors | White, Colorless, Pale blue, Green, Brown, Yellowish |
| Rarity | common |
Geology & background
Hemimorphite forms as a secondary mineral where zinc sulfide ores such as sphalerite are weathered and oxidized by descending groundwater, which dissolves zinc and redeposits it as hemimorphite in cavities and fractures within the host limestone or dolomite. Historic zinc districts such as the Tri-State mining district of Missouri, Kansas, and Oklahoma, along with Mexico's Santa Eulalia and Mapimi deposits, produced exceptional hemimorphite specimens showing sprays of bladed crystals and botryoidal crusts. It commonly occurs alongside smithsonite, calcite, and galena in these oxidized zinc ore zones.
Collectors distinguish hemimorphite from the similar-looking smithsonite mainly through crystal habit, since hemimorphite typically forms distinct bladed or fan-shaped crystal sprays while smithsonite favors rounded, botryoidal crusts. Fine blue hemimorphite specimens from Mexico, showing radiating crystal sprays on a matrix, rank among the most desirable secondary zinc mineral specimens on the collector market. Because the mineral is moderately fragile, careful handling and padded storage help preserve the delicate crystal terminations that make top specimens valuable.
How to identify Hemimorphite
Hemimorphite forms thin, bladed, fan-shaped crystals or botryoidal crusts, typically colorless, white, pale blue, or greenish, with a vitreous to silky luster. Its streak is white, hardness is about 4.5 to 5, and it shows distinct cleavage in one direction, though this is often hard to observe in the fine crystal sprays typical of the mineral. It reacts to acid much more slowly than the carbonate mineral smithsonite, which it closely resembles, making a dilute acid test the most reliable way to separate the two secondary zinc minerals in hand specimen.
- Compare the specimen's color, luster, crystal habit, grain size, streak, and locality before confirming.
- Use multiple photos when possible, including a fresh surface and a close view of texture.
Where Hemimorphite is found
Reported from multiple localities worldwide; verify locality against specimen provenance when available.
How much is Hemimorphite worth?
| Entry-level specimen | $2 |
|---|---|
| Typical collector specimen | $20 |
| Premium specimen | $150+ |
Value depends on size, crystal quality, color, locality, rarity, damage, and provenance.
Common uses
- Collector specimens
- Education
- Field identification
- Industrial or lapidary use when suitable
Interesting facts
- Hemimorphite gets its name from crystals that grow with different faces on opposite ends of the same axis, a trait called hemimorphism.
- The mineral was historically confused with smithsonite for so long that both were once grouped together under the miner's term calamine.
- Some hemimorphite crystals show weak pyroelectric properties, developing a faint electrical charge when heated or cooled.
Care & safety
Handle as a collector specimen until hardness, cleavage, and fracture are verified.
Avoid inhaling dust. Do not cut, grind, or polish unknown specimens without eye protection and a proper respirator.
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