rectangular-cut phosgenite - Namibia
rectangular-cut phosgenite - Namibia

Phosgenite Value, Price, and Jewelry Information


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.

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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.

rectangular-cut phosgenite - Namibia
Rectangular step-cut phosgenite, 2.15 cts, 7.6 x 5.1 mm, Namibia. © The Gem Trader. Used with permission.
phosgenite - United Kingdom
Phosgenite specimen, 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.

phosgenites and cerussites - 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

HardnessSGFluorescence in UVRefractive IndexOptic Character
Anglesite2.5-36.30-6.39Weak yellowish.a = 1.877; b = 1.883; γ = 1.894Biaxial (+)
Cerussite3-3.56.55Can be yellow in LW. Pale blue/green in SW.a = 1.804; b = 2.076; γ = 2.079Biaxial (-)
Phosgenite2-36.13Strong yellowish.o = 2.114-2.118; e = 2.140-2.145Uniaxial (+)

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.

  • phosgenite and galena - normal light
  • phosgenite and galena - UV light

    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.
    radiant cut - Morocco
    Dark "cocoa" brown, emerald radiant-cut, phosgenite, 2.89 cts, 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.

    rough and cut set - Sardinia
    At 37.66 cts, the modified rectangular brilliant-cut phosgenite in this rough and cut set is a giant for the species. Monteponi Mine, Sardinia, Italy. © Rob Lavinsky, www.iRocks.com. Used with permission.

    Care

    Phosgenites contain lead. When cutting this material, avoid ingesting or inhaling particles and wash your hands. For more information, consult our articles on lapidary health hazards and safety tips and toxic and radioactive gems. Since the material is so soft, jewelry use isn't recommended.

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

    Joel E. Arem, Ph.D., FGA

    Dr. Joel E. Arem has more than 60 years of experience in the world of gems and minerals. After obtaining his Ph.D. in Mineralogy from Harvard University, he has published numerous books that are still among the most widely used references and guidebooks on crystals, gems and minerals in the world.

    Co-founder and President of numerous organizations, Dr. Arem has enjoyed a lifelong career in mineralogy and gemology. He has been a Smithsonian scientist and Curator, a consultant to many well-known companies and institutions, and a prolific author and speaker. Although his main activities have been as a gem cutter and dealer, his focus has always been education. joelarem.com


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