Mixed cushion-cut friedelite, 2.97 cts, 10 x 8 mm, Franklin, New Jersey. © The Gem Trader. Used with permission.
Friedelite is not abundant, and gem-quality material is rarely seen even in large collections. Faceted gems are true collector’s items.
Friedelite Information
| Data | Value |
|---|---|
| Name | Friedelite |
| Crystallography | Monoclinic. Crystals are tabular, needlelike, hemimorphic, and very rare. Usually massive, fibrous aggregates, cryptocrystalline. |
| Refractive Index | 1.625-1.664 |
| Colors | Pale pink to dark brownish red, red, brown, orange-red. |
| Luster | Vitreous. |
| Hardness | 4-5 |
| Fracture | Uneven |
| Specific Gravity | 3.04-3.07 |
| Birefringence | 0.030 |
| Cleavage | Perfect 1 direction |
| Luminescence | May be reddish in LW and SW; some material green (SW) and yellow (LW). |
| Luminescence Present | Yes |
| Luminescence Type | Fluorescent, UV-Long, UV-Short |
| Transparency | Translucent to opaque. |
| Absorption Spectrum | Broad band at 5560 and also 4560 (indistinct); spectrum not diagnostic. |
| Formula | (Mn, Fe)8Si6O18(OH, CI)4 · 3H2O |
| Optics | o = 1.654-1.664; e = 1.625-1.629. Uniaxial (-). |
| Optic Sign | Uniaxial - |
| Etymology | Named after the French chemist and mineralogist, Charles Friedel. |
| Occurrence | In manganese deposits. |
This 4 x 3 cm carpet of friedelites on a matrix of franklinite, calcite, and willemite contains individual crystals that measure just over 1 mm in size. Sterling Mine, Sterling Hill, Ogdensburg, Franklin Mining District, Sussex Co., New Jersey, USA. © Rob Lavinsky, www.iRocks.com. Used with permission.
Comments
Lovely friedelite cabochons cut from Franklin, New Jersey material show rich, brownish red colors, while cabs cut from material from the deep manganese mine at Kuruman, South Africa show rose-red colors. Cut stones from both these locations are usually translucent. However, gem cutters have faceted very little of this material.
Friedelite belongs to the pyrosmalite mineral group, which includes schallerite and pyrosmalite.
Identifying Characteristics
Refractometer readings usually show a shadow edge at about 1.645.
Synthetics
No known synthetics.
Sources
Franklin, New Jersey produces gem-quality material, typically brownish and cryptocrystalline, that looks like fibrous chalcedony. Seams of the material at this deposit range up to 2 inches wide. Most gem-quality friedelites come from this location.
Kuruman, South Africa produces massive, dark rose-red material.
Other notable sources of this mineral include the following:
- Austria; Adervielle, France; Kazahkstan; Orebro, Sweden.
Stone Sizes
Translucent stones can normally range up to 1 to 5 carats in size. Although cabochons can be cut to about 30 x 40 mm, larger stones lose any transparency.
Care
You’re more likely to find friedelites, if at all, in mineral collections than in jewelry collections. These gems have significantly lower hardness (4-5) than more common jewelry stones. So, store them separately from other gems to avoid contact scratches. Use protective settings for ring wear. However, necklace and earring use should pose fewer risks. Clean these gems only with a soft brush, mild detergent, and warm water. Consult our gemstone jewelry cleaning guide for more recommendations.
Friedelite: Franklin, New Jersey (1.74). Photo © Joel E. Arem, PhD, FGA. Used with permission.
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