Scorodite: Tsumeb, Namibia (1.0). Photo © Joel E. Arem, PhD, FGA. Used with permission.
With lovely colors and intense pleochroism, faceted scorodite is a prize for collectors of the rare and unusual. However, it’s too soft for jewelry use.
| Data | Value |
|---|---|
| Name | Scorodite |
| Is a Variety of | Variscite |
| Colors | Pale grayish green, yellowish brown to brown, colorless, blueish green, blue, violet. |
| Crystallography | Orthorhombic. Crystals pyramidal, tabular, prismatic; massive, crusts. |
| Refractive Index | Varies by locality, 1.738-1.816. See "Identifying Characteristics" below. |
| Luster | Vitreous to resinous. |
| Hardness | 3.5-4 |
| Fracture | Subconchoidal |
| Specific Gravity | 3.28-3.29 |
| Birefringence | Varies by locality, 0.027-0.031. See "Identifying Characteristics" below. |
| Cleavage | Imperfect |
| Dispersion | Relatively strong. |
| Luminescence | None. |
| Luminescence Present | No |
| Transparency | Translucent to Semi-Transparent. |
| Absorption Spectrum | One line at 4500, broad absorption in the green (Tsumeb). |
| Phenomena | Color change (very rare). |
| Formula |
Fe3+AsO4 · 2H2O |
| Pleochroism |
Intense: purplish/bluish (Tsumeb). |
| Optics |
Biaxial (+), variable 2V. See “Identifying Characteristics” below. |
| Optic Sign | Biaxial + |
| Etymology |
From the Greek skorodon for “garlic,” because the material emits the typical garlic odor of arsenic when heated. |
| Occurrence |
A secondary mineral resulting from the oxidation of arsenious ores. |
“Scorodite-170221,” Alto das Quelhas do Gestoso Mines, Gestoso, Manhouce, São Pedro do Sul, Viseu District, Portugal. Picture width 1.5 mm. Collection and photograph Christian Rewitzer. Licensed under CC By-SA 3.0.
Scorodite belongs to the variscite mineral group. It forms series as the ferric iron analogue (Fe3+) with mansfieldite (AlAsO4 · 2H2O), yanomamite (InAsO4 · 2H2O), and strengite (FePO4 · 2H2O).
Although not a rare mineral, faceted scorodites are extremely rare. A low Mohs hardness score of 3.5 to 4 and imperfect cleavage make them very susceptible to scratches and blows. Thus, faceted pieces would make interesting collector’s gems rather than practical jewelry stones.
“Scorodite,” Wheal Gorland, St, Day, Cornwall, UK. Photo by the University of Exeter. From the collection of the Royal Cornwall Museum, Truro, Cornwall. Licensed under CC By 2.0.
Rare specimens display color change, from blue-green in daylight to blueish purple or grayish blue in incandescent light.
Scorodites may have a greenish-white streak. Please note that streak testing may harm or destroy your specimen. Conduct it on a piece of rough, never a finished gem, only as a last resort.
|
α |
β |
γ |
Birefringence |
2V |
|
| Durango, Mexico |
1.784 |
1.795 |
1.814 |
0.030 |
75° |
| Idaho |
1.738 |
1.742 |
1.765 |
0.027 |
60° |
| Oregon |
1.741 |
1.744 |
1.768 |
0.027 |
40° |
| Tsumeb, Namibia |
1.785 |
1.796 |
1.816 |
0.031 |
75° |
Mansfieldite, yanomamite, and strengite occur far more rarely than their fellow series member scorodite. Accordingly, faceted examples of these minerals, like this pear-cut mansfieldite, are even rarer than scorodites. 2.99 cts, 12.6 x 7.8 mm, Algeria. © Rob Lavinsky, www.iRocks.com. Used with permission. (Images combined to show details).
Scientists have synthesized scorodite, including crystals, for research into the safe disposal of arsenic. However, there is no known jewelry use of this material.
Consumers may encounter so-called “scorolites” for sale online. Often marketed as “scorolite opals,” they are, in fact, simulants, usually purplish glass or quartz pieces. Occasionally, you might encounter this same material offered as scorodite. Keep in mind that “scorolite” is not a synonym or alternate name for scorodite. Quartz and glass are distinct gemologically from scorodites. (This confusion may stem from a typo in a paper on geo-environmental hazards in groundwater in India).
None known.
“Scorodite,” 2.0 x 1.6 x 0.9 cm, Hezhou, Guangxi Zhuang Autonomous Region, China. © Rob Lavinsky, www.iRocks.com. Used with permission.
Tsumeb, Namibia produces beautiful, pleochroic blue/purplish crystals, some gemmy, up to 25 mm long.
Durango, Mexico and Ouro Preto, Minas Gerais, Brazil also yield fine, blue crystals, some gemmy.
Other notable crystal sources include
An unusual stalactitic growth of scorodite. 7.7 x 6.2 x 1.0 cm, Djebel Debar, Hamman, Meskhootine, Constantine Province, Algeria. © Rob Lavinsky, www.iRocks.com. Used with permission.
Scorodites almost always make small faceted gems. As a reasonable maximum, expect about five carats. However, even that would be very large for the species.
Scorodites just don’t have the wearability to serve as jewelry stones. Furthermore, they’re soluble in acids and contain arsenic. While this shouldn’t pose a problem for wear or display, gem cutters should take precautions to prevent inhaling particles, protect their eyes, and wash their hands while working with scorodites.
Scorodite: Tsumeb, Namibia (1.15, 1.50). Photo © Joel E. Arem, PhD, FGA. Used with permission.
IGS Newsletter
