“Faceted Mellite,” 9.8 x 8.2 mm, Csordakúti Mine, Bicske-Csordakút, Bicske-Zsámbéki Basin, Fejér Co., Hungary, by Didier Descouens. Licensed under CC By 4.0.
Mellite is a rare and unusual organic gemstone. Although soft and fragile, the “honey stone” is quite beautiful when cut.
| Data | Value |
|---|---|
| Name | Mellite |
| Crystallography | Tetragonal. Crystals prismatic, pyramidal; granular, nodular, massive. |
| Refractive Index | 1.509-1.541 |
| Colors | Honey yellow, reddish, brownish, rarely white. |
| Luster | Resinous to vitreous. |
| Hardness | 2-2.5 |
| Fracture | Conchoidal |
| Specific Gravity | 1.58-1.64 |
| Birefringence | 0.028-0.032 |
| Cleavage | Indistinct |
| Luminescence | Dull white or medium light blue fluorescence in shortwave (SW) ultraviolet light (UV). Lemon yellow in longwave (LW) UV. German material may fluoresce medium light blue. Russian material may fluoresce weak brown in SW. |
| Luminescence Present | Yes |
| Luminescence Type | Fluorescent, UV-Long, UV-Short |
| Transparency | Transparent to translucent. |
| Absorption Spectrum | Not diagnostic. |
| Formula | Al2C6(COO)6 · 18H2O (aluminum mellitate). |
| Pleochroism | Weak; yellow/yellow-brown. |
| Optics | o = 1.539-1.541; e = 1.509-1.511. Uniaxial (-). May show anomalously biaxial character. See “Identifying Characteristics” below. |
| Optic Sign | Uniaxial - |
| Etymology | From the Latin word mel, meaning "honey," alluding to the gem's color. |
| Occurrence | A secondary mineral in brown coals and lignites. |
“Mellite,” 2.2 x 1.7 x 1.7 cm, Luschitz, Bilina, Usti Region, Bohemia, Czech Republic. © Rob Lavinsky, www.iRocks.com. Used with permission.
Unlike other organic gemstones, such as pearls and coral, whose formation involves living creatures, mellite is an organic gem material formed by inorganic processes. It forms in association with lignite (brown coal) from compressed decayed plant matter and aluminum.
Of course, like its namesake, mellite occurs in attractive honey yellow, reddish, and brownish colors. Occasionally, white specimens also emerge.
In addition to its unusual origins, mellites have a number of interesting properties.
With a very low hardness of 2 to 2.5, mellites can be scratched by a copper coin. These gems are also sectile, which means you could cut them with a knife.
Mellite crystals also exhibit the pyroelectric effect. They generate an electric current when heated.
Although mellites have a uniaxial optic character, anomalously biaxial specimens may occur.
Few well-known gems within mellite’s color range and hardness are likely to be confused with it. Cinnabar has a similar hardness but a far higher specific gravity (SG). Amber and ulexite have hardness and SG values close to mellite. However, these gems differ optically. Amorphous amber has no birefringence. While fibrous ulexite is birefringent, cut specimens usually showcase a cat’s eye or the unusual “TV effect.” Mellites don’t display these effects.
“Mellite,” 5.7 x 4.0 x 3.1 cm, Csordakúti Mine, Bicske-Zsámbéki Basin, Fejér Co., Hungary. © Rob Lavinsky, www.iRocks.com. Used with permission.
Scientists have synthesized mellite for research into geochemistry. However, there is no known use of this material for jewelry purposes.
Although you might find “synthetic” mellites or honey stones for sale online, these materials are, strictly speaking, simulants or imitations, most likely glass. While gemology distinguishes between synthetics and simulants, these words both carry strong connotations of “fakeness” in everyday usage. Thus, people often use the terms synonymously.
No known gem treatments.
Only a few locations produce mellites.
“Mellite,” 1.7 x 1.6 x 1.0 cm, Tula, Tul’skaya Oblast’, North-Western Region, Russia. © Rob Lavinsky, www.iRocks.com. Used with permission.
Mellites almost always weigh in on the small side, from 1 to 3 carats. Some cut specimens can show a high degree of transparency.
Truly one of the most interesting rare gemstones, mellite would make a challenging jewelry stone. Reserve any pieces for occasional wear and avoid impacts. Store them separately from other harder jewelry stones to prevent contact scratches. Clean mellites only with a soft brush, mild detergent, and warm water. Consult our gemstone jewelry cleaning guide for more recommendations.
Mellite: Germany (0.42). Photo © Joel E. Arem, PhD, FGA. Used with permission.
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