Phosgenite Gemstone: Properties, Meanings, Value & More

Phosgenite is a lesser-known, rare gemstone usually found as pale brown or colorless crystals. The stone is mostly known among collectors who seek out rare faceted phosgenites and high-quality crystal rough.

Some of phosgenite’s notable properties? Unique crystal symmetry, diamond-like luster, and intriguing ancient uses.

Unfortunately, phosgenite’s cleavage, rarity, and low, variable hardness make faceted gemstones rare.

That doesn’t mean phosgenite has nothing to offer, though. We here at Gem Rock Auctions have learned over our decades in the industry that no gemstone is worth overlooking.

Today, we’ll be sharing our knowledge to fill you in on all things phosgenite, from its mineral and gemstone properties to its history, prices, and more!

Pictured above: Relatively large, thick, and gemmy phosgenite crystal from Italy | Image credit: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0

About Phosgenite Stone

Phosgenite is a rare semi-precious gemstone found colorless or in pale shades of gray, pink, brown, yellow, or green.

The stone was previously known by various monikers:

• Corneous Lead / Corneous Lead Ore

• Horn Lead

• Galenoceratite

• Kerasine

• Lead chlorocarbonate

• Lead murio-carbonate

• Cromfordite

Many of these monikers reference being horn-like, which had to do with phosgenite’s sectile and flexible tenacity.

Sectile materials can be smoothly cut into thin shavings; flexible materials are bent without breaking, then remain bent. Shavings or scrapings of phosgenite are curved like a horn.

Phosgenite Uses

Today, phosgenite minerals don’t have many industrial applications. However, synthetic phosgenite has been researched both for creating new versions (like a synthetic bromine analogue) and studying past uses of synthetic phosgenite.

Most notably, researchers have found synthetic phosgenite in ancient cosmetics from Egypt and China.

We’ll discuss this more in the Phosgenite History section, but the research was significant for proving that ancient chemical techniques were more advanced than scientists previously thought.

Pictured above: Phosgenite specimen from British Museum of Natural History collection | Image credit: Rock Currier, CC-BY-SA-3.0

Phosgenite Specifications & Characteristics

Phosgenite is a lead carbonate chloride (or “chlorocarbonate”) with the formula Pb2CO3Cl2. The molecular weight of phosgenite is 545.315 gm.

The crystal symmetry of phosgenite is unique. It’s tetragonal and trapezohedral (8 trapezohedral faces), but it doesn’t have a center of symmetry or mirror planes.

In terms of habits, phosgenite crystals are usually prismatic. The crystals can also be tabular and thick or thin, but these are rarer.

Phosgenite’s crystal faces are usually bright and smooth with vertical striations. Some crystals have pointed terminations. Occasionally, phosgenite crystals form with a helical (helix-like) twist at the principal or tetrad axis.

Alternatively, phosgenite can occur in massive or granular habits.

The tenacity of phosgenite is mostly sectile, but it’s flexible in directions perpendicular to [001]. Mechanical deformation (bending and staying bent) can make the normally uniaxial (+) mineral appear weakly biaxial.

Phosgenite properties listed:

• Mohs hardness: 2-3, varies with direction; Hardness on {110} is less parallel to [001] than perpendicular to [001]

• Color: Colorless, white, yellow, brownish-yellow, brown, green, pink, pinkish-yellow, violet, violet-gray, gray

• Crystal structure: Tetragonal

• Luster: Adamantine, vitreous, sub-adamantine, or greasy

• Transparency: Translucent to transparent

• Refractive index: 2.114-2.145

• Density: 6.12-6.15

• Cleavage: Distinct/Good on {001} and {110}, Indistinct on {100}

• Fracture: Conchoidal

• Streak: White

• Luminescence: Usually fluorescence - Strong yellow or orange in LW-UV (with phosphorescence); Yellow in SW-UV, X-rays, and electron beams (cathode rays)

• Pleochroism: Present but weak to very weak - reddish and greenish in thick sections

• Birefringence: 0.026-0.028

• Dispersion: Strong

Pictured above: Figure of ancient lead pot (A) with synthetic phosgenite found inside | Image credit: Nature, Recipes of Ancient Egyptian kohls more diverse than previously thought

Phosgenite History

Phosgenite was originally found in 1800 in a lead mine at Cromford in England, UK, now the type locality.

The name “phosgenite” came from German mineralogist & professor August Breithaupt in 1841.

Breithaupt chose the name (initially as phosgen-spath in 1832) after the organic compound “phosgene,” a carbon oxychloride (or carbonyl dichloride) with the formula COCl2, because the mineral contains chlorine, carbon, and oxygen.

Other references to the mineral with different names were:

1. Horn Lead: As hornblei in German, from German mineralogist Dietrich Ludwig Gustav Karsten in 1800

2. Hydrochloric Acid Lead Ore / Lead Chlorocarbonate: As salzsaures bleierz in German; From German chemist Martin Heinrich Klaproth in 1802

3. Corneous Lead / Corneous Lead Ore: From Scottish naturalist & mineralogist Robert Jameson in 1804; Note: “Corneous” means horn-shaped

4. Kerasine: From French mineralogist & geologist François Sulpice Beudant in 1832

5. Galenoceratite: For galena, lead sulfide, and ceratite, meaning horn; From German mineralogist, geologist & paleontologist Ernst Friedrich Glocker in 1847

6. Cromfordite: For discovery location in Cromford, England; From British scientists Robert Philips Greg and William Garrow Lettsom in 1858

Synthetic phosgenite, however, goes back even further.

Synthetic Phosgenite Since Ancient Times

Synthesizing phosgenite dates back centuries.

In 1948, the first discovery was presented: ancient phosgenite found in an ancient lead pot in Wookey Hole, UK.

Philippe Walter and other French researchers at the Louvre Museum published an investigation in 1999 of ancient Egyptian kohl eye makeup powders dating from 2000 to 1200 BC.

The French researchers (and later, radiocarbon dating) concluded that phosgenite (and laurionite) present in the powders must have been synthetically created by Egyptians.

According to British chemist Steve Plant in 2014, ancient Egyptians also used synthetic phosgenite medicinally for skin and eye problems.

Phosgenite Healing Properties

As an often brown healing stone, phosgenite has the grounding and protective properties of other brown gemstones. It’s also a root (base) chakra stone.

Other purported healing properties of phosgenite include:

• Raising self-awareness

• Decreasing stress & anxiety

• Treating memory problems like dementia

• Stimulating cerebral activity for greater focus and problem-solving

• Encouraging resilience and hope

• Offering mental clarity

Pictured above: Clear phosgenite crystal from Greece; Christian Rewitzer collection | Image credit: Christian Rewitzer, CC-BY-SA-3.0

Phosgenite Gemstone Properties

Besides their rarity, phosgenite gemstone value also depends on color, cut, clarity, transparency, and carat weight.

Color

Most phosgenite crystals are white to gray, and faceted phosgenites are typically yellowish-brown. Rarer hues like green, pink, or violet can be more valuable.

Pale shades are common, making any richer hues more sought-after.

Phosgenite in UV light that shows strong yellow fluorescence may also be more valuable.

Cut

Besides the scarcity of facetable material, phosgenite’s multiple cleavage directions, low Mohs hardness, and difficult tenacity make the stone complicated to cut.

As such, faceted phosgenites are rare, valuable finds.

Phosgenite is more often cut into cabochons. Most often, phosgenite for sale is rough (uncut).

Clarity & Transparency

Clarity describes the degree of visible inclusions in a gemstone, which can lower its transparency and value. Even heavily included faceted phosgenites will have value, but eye-clean options are extremely valuable.

Potential inclusions or visible flaws on phosgenites are:

• Negative crystals (e.g. anglesite)

• Zoning

• Polish marks

Higher transparency also raises phosgenite’s value.

Carat Weight & Size

Faceted phosgenites are rarely over 2 carats. You can find rare ones for sale up to 10 carats, and collector options reaching 37.66 carats.

The largest phosgenite crystals come from Tasmania and Italy, including the largest known phosgenite crystal (Italian) displayed at the Rice Museum in Oregon, USA.

Pictured above: Extremely unusual phosgenite crystal from Italy that's oddly formed but complete all around with minor matrix inclusions, exceptionally gemmy interior | Image credit: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0

Phosgenite Formation & Sources

How is phosgenite formed? Phosgenite is a secondary mineral, usually forming when galena undergoes oxidation. It also forms when other primary lead minerals react with sea water or chlorine sources.

The mineral is typically found in hydrothermal lead deposits, particularly surface zones or areas affected by sea water.

Phosgenite can easily alter into cerussite; it’s often found partially replaced by cerussite.

Geographically, where is phosgenite found?

Mining Locations

The best source for phosgenite gemstone material is Sardinia, Italy. Morocco and Namibia also produce facetable crystals.

Other phosgenite sources worth noting are:

Australia

Greece

Mexico

Poland

Russia

Siberia

Tasmania

Tunisia

UK (England)

USA (Arizona, California, Colorado, Massachusetts, New Mexico)

What prices can you expect for phosgenite gemstones?

Pictured above: Sharp, ultra-gemmy phosgenite crystal from Italy with mirror-like luster and light amber coloring | Image credit: Rob Lavinsky, iRocks.com – CC-BY-SA-3.0

Phosgenite Price & Value

Phosgenite’s rarity is reflected in its prices, particularly for cut gemstones.

Faceted phosgenite gemstones are generally around $20 to $270 per carat or about $75 to $1,200 total.

Phosgenite cabochons are about $200 to $300 per carat or $330 to $430 total.

The prices of rough phosgenite vary the most. The priciest options are transparent, large crystal clusters, which go for $375 to $6,000.

Smaller phosgenite crystals and specimens go for $40 to $200.

Phosgenite Care and Maintenance

Proper gemstone care is essential for keeping both you and your phosgenite unharmed.

Phosgenite contains lead, which is toxic to ingest or inhale. Its softness makes it easier to inhale the lead from scratched-off fibers.

The danger is more present for lapidarists (gem cutters), who should take extra safety precautions by wearing a mask and cutting phosgenite with a liquid medium.

For gem buyers, handle phosgenite carefully and wash your hands after.

Store phosgenite in an enclosed case away from anyone who might put it in their mouths, like children or pets.

Read our safety tips for handling toxic gemstones and minerals for more guidance.

Phosgenite will slowly decompose in cold water and dissolve in dilute nitric acid. Keep it away from both.

Carefully clean phosgenite with a soft, microfiber cloth very gently. Keep phosgenite away from other gemstones to avoid scratches.

Ready to Pick the Phosgenite for You?

Phosgenite is a rare gem with hidden mysteries, from subtle colors to ancient creations and even twisted crystal shapes!

Whether you’re a collector or just a gem lover, we highly recommend considering this rare beauty for your collection.

Buy phosgenite and other unique gemstones from our extensive gem collection today!