This brownish red staurolite is lighter than typical for these gems. 1.67-ct, 9.1 x 7.0 x 2.9 mm, oval cut, Brazil. © ARK Rare Gems. Used with permission.
Staurolite crystals in opaque cross shapes are popular gemstones. However, this material is very rarely transparent or facetable. These dark colored gems would make very durable jewelry pieces.
| Data | Value |
|---|---|
| Name | Staurolite |
| Crystallography | Monoclinic (pseudo-orthorhombic). Crystals prismatic, typically twinned at 60° or 90°, the latter termed fairy crosses; massive. |
| Refractive Index | 1.739-1.761 |
| Colors | Dark brown, reddish brown, yellowish brown, brownish black. |
| Luster | Vitreous to resinous. |
| Hardness | 7-7.5 |
| Fracture | Conchoidal |
| Specific Gravity | 3.65-3.83 |
| Birefringence | 0.011-0.015 |
| Cleavage | Distinct 1 direction |
| Dispersion | 0.023 |
| Luminescence | None. |
| Luminescence Present | No |
| Enhancements | Imitation staurolites may be pockmarked artificially to simulate natural weathering; imitations may also be oiled or dyed to darken them. |
| Typical Treatments | Dyeing, Oiling |
| Transparency | Opaque to translucent, transparent (rare) |
| Absorption Spectrum | Not diagnostic. Weak band at 5780, strong at 4490. See "Identifying Characteristics" for zincian staurolite. |
| Phenomena | Color change |
| Formula | (Fe,Mg,Zn)2Al9Si4O23(OH) + Zn or + Co. |
| Pleochroism | Distinct: colorless/yellow or red/golden yellow. |
| Optics | a = 1.739-1.747; β = 1.745-1.753; γ = 1.752-1.761. Biaxial (+), 2V = 82-90°. Indices increase with iron content. |
| Optic Sign | Biaxial + |
| Etymology | From the Greek stauros and lithos, meaning “stone cross.” |
| Occurrence | Staurolite is a mineral of metamorphic rocks, such as schists and gneiss. |
| Inclusions | Crystals (garnet, quartz), may have surface cavities. |
Cut staurolites, Minas Gerais, Brazil. Gem cutting by Afonso Marques. Photo by Eurico Zimbres. Licensed under CC By-SA 3.0.
Staurolites can form as twinned crystals at either 60° or 90°, creating interesting natural cruciform pieces. Thus, these stones are popularly called “fairy crosses” or “fairy stones.” They’ve inspired a number of symbolic associations over time. According to George F. Kunz, the noted mineralogist and folklorist, a Virginia legend holds that the tears of fairies crying at the news of Christ’s death turned into these stones. People from many cultures throughout history have also treated cross-shaped staurolites as good luck charms.
“Fairy Stones,” both unpolished and polished, Fairy Stone State Park. Photo by Virginia State Parks. Licensed under CC By 2.0.
Crystals with both 60° and 90° twinning are extremely rare.
Collectors highly prize faceted staurolites. However, such gems are rarely transparent, always small, dark in color, and lack fire or dispersion. Their interest lies in their extreme scarcity.
Staurolite rough and cut set, Keivy, Keivy Mountains, Kola Peninsula, Russia. 4.3 x 3.1 x 2.3 cm (crystal), 1.08-ct (brilliant pear-cut gem, source unknown). © Rob Lavinsky, www.iRocks.com. Used with permission. (Gem photo cropped to show detail and slide show created to facilitate comparison).
Though very rare, zinc-bearing staurolites have lighter colors and make more attractive cut gems.
A deep blue, strongly pleochroic cobalt-bearing staurolite from Lusaka, Zambia.
Scientists have synthesized staurolites for petrological and crystallographic research. However, there is no known jewelry use for this material.
Staurolite crystals aren’t rare. However, people have created simulations of cruciform crystals due to their popular symbolic associations. The manufacture of faux “fairy crosses” goes back at least a century. In the 1910s and 1920s, the mineralogist Joseph K. Roberts examined specimens from Georgia, Tennessee, and Virginia and learned how some were likely created. In a 1934 article in American Mineralogist, Roberts noted that 90° “Roman Cross” shapes dominated the market, despite being the rarer variety. He discovered that many were cut from much softer talcose material, filed into shape, and then soaked in linseed or other oils to darken them. (A GIA note from 1963 describes a similar talcose imitation dipped in paraffin).
Apparently, the demand for transparent, facetable staurolite hasn’t yet generated the same level of industrious deception.
Cruciform staurolites may be filed to improve the appearance of their terminations or smooth out surface cavities. Although weathering may give natural specimens a pitted appearance, Roberts also noted in his 1934 article that some imitations received artificial pockmarks to appear more natural!
Staurolites, Brittany, France, from the collection of the National Museum, Prague, Czech Republic. Photo by Karelj. Public Domain.
Brazil and Switzerland will occasionally produce facetable crystals.
Various locations in the United States yield “fairy crosses.” Visitors to Fairy Stone State Park in Virginia and Blanchard Dam, near Little Falls, Minnesota, may gather them off the ground.
Other notable crystal sources include
“Cross twin” staurolite, J. M. Spear farm, Bluff Creek, Ball Ground, Ball Ground District, Cherokee Co., Georgia, USA, 4.5 x 4.5 x 1.4 cm. © Rob Lavinsky, www.iRocks.com. Used with permission.
Always tiny, cut staurolites from Brazilian or Swiss material generally weigh under 2 carats.
With a hardness of 7-7.5, faceted staurolites would make durable jewelry stones. However, stones with cavities associated with fractures that extend to the surface may have structural weakness. These may also collect dirt and grime. (Staurolite surface cavities typically occur when mineral inclusions weather out of the stone). Stay on the safe side and clean any staurolites, faceted or natural crystals, with a soft brush, mild detergent, and warm water. Otherwise, these gems require no special care. Consult our gemstone jewelry cleaning guide for more recommendations.
Staurolite: Brazil (0.50). Photo © Joel E. Arem, PhD, FGA. Used with permission.
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