Phosgenite Value, Price, and Jewelry Information

large phosgenite - rectangle brilliant cut
An unusually large, faceted phosgenite with a rich cognac-like hue from the Monteponi Mine, Sardinia, Italy. 37.66 carats, modified rectangle brilliant cut. © Rob Lavinsky, www.iRocks.com. Used with permission.

Rare phosgenite typically shows pale colors. This material is difficult to cut and too soft for jewelry wear. However, its strong yellowish fluorescence appeals to collectors of unusual gemstones.

Phosgenite Value

The International Gem Society (IGS) has a list of businesses offering gemstone appraisal services.

Phosgenite Information

DataValue
NamePhosgenite
Crystallography Tetragonal; Crystals prismatic, thick and tabular; massive, granular.
Refractive Index 2.114-2.145
Colors Colorless, white, yellowish white, gray, shades of brown, greenish, pinkish.
Luster Adamantine to greasy.
Polish Luster Adamantine.
Fracture Conchodial
Hardness 2-3, varies with direction.
Specific Gravity 6.13.
Birefringence 0.028
Cleavage Distinct 1 direction, Good
Luminescence Strong yellowish fluorescence in UV and X-rays.
Transparency Transparent to translucent.
FormulaPb2CO3Cl2.
Pleochroism Very weak, reddish/greenish, only in thick pieces.
Optics o = 2.114-2.118; e = 2.140-2.145. Uniaxial (+). May be anomalously biaxial.
EtymologyFrom phosgene, a name for the compound COCl2 (carbonyl chloride) because the mineral contains C, O, and Cl.
OccurrenceA secondary mineral in lead ore deposits.
phosgenite - United Kingdom
“Phosgenite,” Wallclose Mine, Cromford, Derbyshire, England, UK, from the collection of the British Museum of Natural History. Photo by Rock Currier. Licensed under CC By 3.0.

Comments

Lapidaries can cut massive phosgenite into interesting cabochons of various colors, up to the size of the rough (several inches). However, faceted pieces are more rarely encountered, not simply due to the material’s scarcity. Phosgenites can have directions of variable (and low) hardness (2-3) and distinct to good cleavage. Although this gem can have an adamantine, diamond-like luster, it’s also difficult to polish. If you take into account its flexible and sectile properties, it just doesn’t make a practical jewelry stone.

Identifying Characteristics

While phosgenite usually occurs colorless or in soft shades of yellow, gray, brown, pink, or green, it has a strong yellowish fluorescence under both ultraviolet light (UV) and X-rays. This fluorescence and its relatively high specific gravity (SG) of 6.13 help to distinguish it from stones of similar range and hardness. In fact, phosgenite has a much greater density than two more popular gems with a similar range of colors and hardness: amber (1.08) and mellite (1.64).

However, two other rarely faceted collector’s gemstones have a comparable range of colors, hardness, and SG. Like phosgenite, anglesite and cerussite can be colorless as well as white, grayish, yellowish, or greenish. Their fluorescence under UV light can also appear yellowish. Furthermore, these minerals can crystalize in close association.

phosgenite with cerussite - Greece
“Phosgenite with cerussite,” Thorikos Bay slag locality, Thorikos area, Laurium District slag localities, Laurium District, Attica Prefecture, Greece. Photo by Didier Descouens. Licensed under CC By-SA 4.0. (The transparent prismatic crystals are phosgenites; the acicular, “needle-like” crystals are cerussites;).

Comparison of Selected Physical and Optical Properties of Anglesite, Cerussite, and Phosgenite

Hardness SG Fluorescence in UV Refractive Index Optic Character
Anglesite 2.5-3 6.30-6.39 Weak yellowish. a = 1.877; b = 1.883; γ = 1.894 Biaxial (+)
Cerussite 3-3.5 6.55 Can be yellow in LW. Pale blue/green in SW. a = 1.804; b = 2.076; γ = 2.079 Biaxial (-)
Phosgenite 2-3 6.13 Strong yellowish. o = 2.114-2.118; e = 2.140-2.145 Uniaxial (+)

A refractive index and an optic character reading with a refractometer and/or polariscope may be the most effective way to distinguish these gems. However, keep in mind that phosgenites may be anomalously biaxial. Thick pieces of phosgenite (not all specimens) may have weak pleochroism, while anglesite and cerussite don’t.

The yellow fluorescence of this gemmy phosgenite crystal on galena is more marked in its upper centimeter. 4.2 x 3.0 x 3.0 cm. Monteponi Mine, Iglesias, Sardinia, Italy. © Rob Lavinsky, www.iRocks.com. Used with permission.

Synthetics

Scientists have synthesized phosgenite for various purposes for centuries. In the February 2014 newsletter of the British Micromount Society, Steve Plant describes various manufacturing methods, from the time of the Ancient Egyptians (who used synthetic phosgenite for makeup) through 19th and early 20th century procedures to current techniques. Although lab-created crystals do exist, there is no known jewelry use for this material.

Enhancements

None known.

Sources

Monteponi, Sardinia, Italy produces fine, yellow-brown crystals up to 5 inches across, some with facetable areas.

Other notable sources include the following:

  • United Kingdom: Matlock and Cromford, Derbyshire, England (type locality).
  • United States: Arizona; California; Colorado; Massachusetts; New Mexico.
  • Australia; Laurium, Greece; Morocco (some cuttable); Tsumeb, Namibia (some cuttable); Tarnow, Poland; Russia; Tasmania; Tunisia.
faceted phosgenite - Morocco
2.89-ct phosgenite, dark brown “cocoa,” emerald radiant cut, 7.5 x 5.8 mm, Morocco. © The Gem Trader. Used with permission.

Stone Sizes

Rare faceted specimens almost always weigh less than 2 carats. Typically from Sardinia, these gems usually have a yellowish brown color. However, a few larger stones exist, some up to about 10 carats. (The 37.66-ct faceted phosgenite at the top of the article is a giant for this species).

Care

Phosgenites contain lead. When cutting this material, avoid ingesting or inhaling particles and wash your hands.

Jewelry use is not recommended.

Faceted phosgenite - Sardinia
Phosgenite: Monteponi, Sardinia, Italy (1.5). Photo © Joel E. Arem, PhD, FGA. Used with permission.