Hemimorphite cabochon, 54.75 cts, 30.6 x 27.6 x 5.5 mm, ’79 Mine, Arizona. © 49erMinerals. Used with permission.
Massive hemimorphite can have a very delicate, blue color. However, it’s seldom cut because not very much has appeared on the market.
| Data | Value |
|---|---|
| Name | Hemimorphite |
| Colors | White, colorless, pale blue, greenish, gray, yellowish, brown. |
| Crystallography | Orthorhombic. Crystals tabular and thin, striated; fan-shaped aggregates. |
| Refractive Index | 1.614-1.636 |
| Luster | Vitreous, silky; dull. |
| Hardness | 4.5-5 |
| Fracture | Even to subconchoidal. |
| Specific Gravity | 3.4-3.5 |
| Birefringence | 0.022 |
| Cleavage | Perfect 1 direction. |
| Luminescence | Weak blueish fluorescence under SW UV. |
| Luminescence Present | Yes |
| Luminescence Type | Fluorescent, UV-Short |
| Transparency | Transparent to opaque |
| Absorption Spectrum | Not diagnostic. |
| Formula |
Zn4Si2O7(OH)2· H2O |
| Pleochroism |
None. |
| Optics |
a = 1.614; β = 1.617; γ = 1.636. Biaxial (+), 2V= 46°. |
| Optic Sign | Biaxial + |
| Etymology |
From the Greek hemi and morphe, meaning “half-form,” in allusion to its crystal form. |
| Occurrence |
A secondary mineral in the oxide zones of ore deposits. |
Hemimorphite: Zacatecas, Mexico (~ 3 inches high). Photo © Joel E. Arem, PhD, FGA. Used with permission.
Hemimorphite is very rare as a faceted gemstone. So far, only Mexico has produced suitable material. However, gem cutters have cut cabochons from material found in many locations.
In the early 19th century, the British mineralogist James Smithson discovered that the zinc ore then known as calamine was composed of hemimorphite and smithsonite. These minerals, along with hydrozincite, are, in fact, distinct minerals despite their external similarities.
Faceted Hemimorphite: Mexico (0.75). Photo © Joel E. Arem, PhD, FGA. Used with permission.
As crystals, hemimorphites show different terminations at each end. Hence the name hemi – morphite, since each end or “half” takes a different “form.”
This gem exhibits the pyroelectric effect. When heated, it generates an electrical charge.
Hemimorphite, Santa Eulalia Dist., Serdan, Chihuahua, Mexico. © Rob Lavinsky, www.iRocks.com. Used with permission.
No known synthetics. However, gemologists have identified artificial simulants, such as partially devitrified glass. (The process of devitrification produces crystals in normally amorphous glass).
Natural gems such as smithsonite, chrysocolla, and turquoise may also resemble hemimorphite. However, these gems possess very different properties and should be distinguished easily. Chrysocolla’s and turquoise’s specific gravities differ significantly from hemimorphite’s. Smithsonite’s specific gravity and optic sign also differ from those of its former partner in calamine.
In Mexico, Mapimi, Durango and Santa Eulalia, Chihuahua can produce transparent crystals up to several inches in length, which may yield stones up to approximately 7-10 carats. Blue crusts are also found. Other Mexican locations produce beautiful gems as well.
This mineral is found in various localities worldwide. Other notable gem-quality sources include the following:
Hemimorphite crystals, Laochang ore field (Laochang Mine), Eastern Sub-District, Gejiu Sn-polymetallic ore field, Gejiu Co., Honghe Autonomous Prefecture, Yunnan Province, China. Photo by Géry Parent. Public Domain.
Gem cutters have cut cabochons up to several inches in length from massive blue material. They’ve also faceted colorless material from Mexico into gems from 1-3 carats in size. Larger stones are very rare.
Due to their relatively low hardness, store these gems separately from other harder, more common jewelry stones, such as quartz. For cleaning, use a soft brush, mild detergent, and warm water only. Consult our gemstone jewelry cleaning guide for more recommendations.
Hemimorphite, ’79 Mine (Seventy-Nine property; McHur prospect), Chilito, Hayden area, Banner District, Dripping Spring Mts, Gila Co., Arizona, USA. © Rob Lavinsky, www.iRocks.com. Used with permission.
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