“0.68-ct Legrandite,” rectangular step cut, 5.4 x 4.3 mm, Mexico. © The Gem Trader. Used with permission.
Too soft for jewelry use, legrandite is a popular collector’s mineral because of its intense yellow color and aesthetic crystal groupings. Transparent, faceted gems are extremely rare.
| Data | Value |
|---|---|
| Name | Legrandite |
| Colors | Yellow, colorless. |
| Crystallography | Monoclinic. Crystals prismatic, also in sprays and fans. |
| Refractive Index | 1.675-1.740 |
| Luster | Vitreous. |
| Hardness | 4.5 |
| Fracture | Uneven |
| Specific Gravity | 3.98-4.04 |
| Birefringence | 0.060. |
| Cleavage | Poor |
| Dispersion | Distinct. |
| Luminescence | None. |
| Luminescence Present | No |
| Transparency | Translucent to transparent. |
| Absorption Spectrum | Not diagnostic. |
| Formula |
Zn2(OH)AsO4 · H2O. |
| Pleochroism |
Colorless to yellow. |
| Optics |
a = 1.675-1.702; β = 1.690-1.709; γ = 1.735-1.740. Biaxial (+), 2V = 50°. |
| Optic Sign | Biaxial + |
| Etymology |
Named after Louis C. A. Legrand, a Belgian mine manager who collected the first specimens. |
| Occurrence |
In vugs in limonite. Uncommon secondary mineral in the oxidized zone of arsenic bearing zinc deposits; rare in granite pegmatite. |
“Legrandite, Limonite,” Ojuela Mine, Mapimí, Mun. de Mapimí, Durango, Mexico. Photo by Géry Parent. Licensed under CC By-ND 2.0.
First described in 1932, legrandite has become one of the loveliest of all rare collector gemstones. Its yellow color is quite distinctive and appealing.
Transparent crystals are usually small in size. The larger the crystal, the more opaque (translucent) it becomes.
The gem’s distinctive yellow color tends to appear splotchy.
“Legrandite” by Ed Uthman. Licensed under CC By 2.0.
None known.
None known.
To date, only Mexico has produced cuttable material. Legrandite was first discovered in the Flor de Peña Mine, Nuevo León, Mexico. However, the best-known gem locality is the Ojuela Mine, Mapimí, Mexico. It produces magnificent crystal clusters, single crystals up to 6 cm long and 7.5 mm thick.
Other notable crystal sources include
“Legrandite (Type Locality),” Flor de Peña Mine, Lampazos, Nuevo León, Mexico, 4.0 x 3.0 x 2.0 cm. © Rob Lavinsky, www.iRocks.com. Used with permission.
The largest faceted legrandites range from 2 to 4 carats in size, although a 10-ct stone has been reported. Still, larger cut stones are great rarities, and even 1-ct gems are hard to find.
Many mineral specimens exist. However, transparent crystals occur very rarely, even at the source locality.
Legrandite: Mexico (~ 2, rough 1½ inches long). Photo © Joel E. Arem, PhD, FGA. Used with permission.
You’re more likely to find legrandites in a mineral collection than a jewelry collection. With a relatively low hardness of 4.5, it has greater susceptibility to scratches than more popular jewelry stones.
Legrandite contains arsenic. While this should not 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 this material.
“Legrandite,” Ojuela Mine, Mapimí, Durango, Mexico, 6.4 x 4.6 x 3.2 cm. © Rob Lavinsky, www.iRocks.com. Used with permission.
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