Mineral
Marcasite
FeS₂Markazit
An iron sulfide with the same formula as pyrite but paler, more brittle and unstable; the stones of “marcasite jewellery” are mostly pyrite.
Also known as: Spear pyrites · Cockscomb pyrites
- Popularly: Common stone
- Important in Türkiye
In short
Marcasite is a pale bronze-yellow mineral (FeS₂) with a metallic lustre, made of iron and sulfur. It has the same chemical formula as pyrite but a different crystal structure: pyrite crystallises in the cubic system, marcasite in the orthorhombic system. Compared with pyrite it is paler, more brittle and much less stable in a damp environment; as it decays it forms sulfuric acid. Its name causes confusion: the stones of jewellery sold as “marcasite jewellery” are in fact usually pyrite.
Photos
How does it form?
Marcasite forms at low temperatures and in strongly acidic conditions: both in sedimentary settings (shales, limestones, low-rank coals) and in veins formed by rising hot solutions. Pyrite, pyrrhotite, galena, sphalerite, fluorite, dolomite and calcite are found with it. Twinning gives it its characteristic cockscomb and spearhead groups.
What is it used for?
Marcasite is not an ore or a gemstone in its own right; it belongs in mineral collections and is the source of the name “marcasite jewellery”. Because it is prone to decay, it is kept protected from damp in museums and collections.
What is marcasite jewellery?
“Marcasite jewellery”, despite its name, is made not of marcasite but of small cut and polished pieces of pyrite, mostly set in silver. Pyrite is chosen because it is more stable and less brittle than marcasite, which can react with moisture to form sulfuric acid. In the 18th century, where the wearing of diamonds was restricted (in Switzerland, for example), such pieces took the place of diamonds; after Prince Albert’s death in 1861, during Queen Victoria’s mourning, they came back into favour among nobles looking for understated jewellery.
In Türkiye
Marcasite occurs in small amounts in the massive sulfide deposits of the Eastern Black Sea. In the Çakmakkaya and Damarköy copper deposits at Murgul in Artvin, a little sphalerite, galena, tetrahedrite and marcasite has been found beside pyrite and chalcopyrite in the stockwork ore veinlets. In the ore of Çayeli in Rize, bornite, tetrahedrite and marcasite occur beside sphalerite, chalcopyrite and pyrite. In the Karabaşvengi iron mineralisation in the Divriği district of Sivas, pyrite, chalcopyrite, pyrrhotite, marcasite, arsenopyrite, sphalerite and galena are reported beside magnetite.
What determines its value?
Marcasite is not valuable as an industrial ore or as a jewellery stone; its tendency to decay limits its uses. For collectors, its worth depends on the form of the crystals (twinned groups such as cockscombs or spearheads), their lustre, freedom from damage and decay, and a famous locality; specimens kept safe from damp hold their value. For pieces sold as “marcasite jewellery”, what counts is not the stone but the metalwork, the age and the condition, because the stone is mostly pyrite.
This information is educational, not buying, selling or investment advice. Value varies enormously with quality and treatment.
How to recognise it
- 1
A fresh surface is tin-white to pale bronze-yellow; it is less golden than pyrite. It darkens in air and may form an iridescent tarnish.
- 2
Its hardness is 6–6.5 (the same as pyrite): a steel knife does not scratch it. It is brittle.
- 3
Its streak (powder colour) is gray or brownish black.
- 4
Crystals are mostly tabular; twinning makes “cockscomb” or “spearhead” groups, and curved crystal faces are common. Pyrite, by contrast, usually forms cubes or pentagonal dodecahedra.
- 5
Its specific gravity (4.9) is very close to pyrite’s (5.0), so it is not distinctive on its own.
- 6
It decays in damp air: crusts of iron sulfate form on the surface, and nearby labels and specimens are eaten away.
Fakes and imitations
What shops usually don’t tell you:
- The stones in jewellery sold as “marcasite jewellery” are not real marcasite but cut and polished pyrite, because marcasite is very brittle and decays in damp conditions, forming sulfuric acid. The name dates from before the scientific definition.
- In cheaper “marcasite” pieces the stones may be glued rather than set; similar jewellery is also made of small pieces of cut steel.
Safety
Marcasite is an iron sulfide. Handling it is generally harmless. In damp conditions, however, it decays much faster than pyrite: iron sulfate and sulfuric acid form, and the acid corrodes labels, boxes and nearby sulfide specimens (“pyrite decay”). Do not touch a specimen coated with a whitish-greenish crust with bare hands; store marcasite specimens somewhere dry, below 60 per cent humidity. Do not heat it; irritating sulfur dioxide gas is released. Do not put it in your mouth, and do not put it in water to make “gem water” or an “elixir”: acid forms as it decays.
Myths and misconceptions
MythThe stones in “marcasite jewellery” are marcasite.
FactThe stones in jewellery sold under this name are mostly cut pyrite. Real marcasite is brittle and unstable and is not used in jewellery; “marcasite” is an old name that was used for such jewellery even before the scientific definition.
MythMarcasite and pyrite are the same mineral.
FactBoth have the formula FeS₂, but their crystal structures differ: pyrite crystallises in the cubic system, marcasite in the orthorhombic system. Marcasite is paler, more brittle and decays much more easily in damp conditions.
What is it believed to be good for?
This section reports beliefs; it is not health information. There is no scientific evidence for these claims and no stone replaces medical treatment.
The meanings people give this stone, and who holds them:
- Jewellery sellers and crystal-therapy sites associate marcasite with wisdom, courage and self-expression.
- The same sources say marcasite lends strength to meditation and increases creativity in the arts.
What science says
There is no scientific evidence that marcasite gives wisdom, courage or creativity. Because the stones of “marcasite” jewellery are mostly pyrite, these claims are often really made for pyrite too. Real marcasite decays in damp conditions, forming sulfuric acid: it should not be put in water to make “gem water” or an “elixir”, and should not be put in the mouth.
Did you know?
The word “marcasite” is, according to the sources, of Arabic or Moorish origin; in the late medieval and early modern periods it was used for all iron sulfides. In today’s sense (orthorhombic iron sulfide) it was defined in 1845.
Marcasite forms at low temperatures and in acidic conditions: in laboratory experiments, below a pH of about 5, marcasite is deposited in preference to pyrite.
Marcasite occurs in chalk beds around Cap Blanc-Nez in France and Dover in England.
Where is it found?
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- Joplin, Missouri, USA · Known localityThe first place the Handbook of Mineralogy names for marcasite; one of its analysed samples came from Joplin (Jasper County) (coordinate is the city centre)
- Cap Blanc-Nez, Pas-de-Calais, France · Known localityMarcasite in chalk beds; mentioned by the Handbook of Mineralogy and Wikipedia
- Dover, Kent, England · Historic sourceThe Handbook of Mineralogy lists the chalk of Kent and the area between Folkestone and Dover; Wikipedia names Dover (coordinate is the town centre)
- Reocín mine, Cantabria, Spain · Known localityWikipedia mentions the cockscomb marcasite formations of the Reocín mine (coordinate is the centre of the Reocín municipality)
- Freiberg, Saxony, Germany · Historic sourceAn old mining town in Saxony that the Handbook of Mineralogy names for marcasite (coordinate is the town centre)
- Santa Eulalia, Chihuahua, Mexico · Known localityA mining district the Handbook of Mineralogy names for marcasite (coordinate is the town of Santa Eulalia)
- Llallagua, Potosí, Bolivia · Known localityA place the Handbook of Mineralogy names for marcasite (coordinate is the town centre)
- Murgul, Artvin, Türkiye · Known localityIn the Çakmakkaya and Damarköy copper deposits, a little marcasite is reported in the stockwork ore veinlets beside pyrite and chalcopyrite (coordinate is the district centre)
- Çayeli (Madenköy), Rize, Türkiye · Known localityIn the mineralogical analysis of the ore, bornite, tetrahedrite and marcasite were found beside sphalerite, chalcopyrite and pyrite (coordinate is the district centre)
- Karabaşvengi, Divriği, Sivas, Türkiye · Known localityA little marcasite is reported beside magnetite in the Karabaşvengi iron mineralisation, about 5 km north-east of the main Divriği iron deposit (coordinate is the district centre)
Locations are approximate to protect sites. Red dots mark places in Türkiye. Open in the big map →
Frequently asked questions
What is marcasite?
Marcasite is a pale bronze-yellow mineral (FeS₂) with a metallic lustre, made of iron and sulfur. It has the same chemical formula as pyrite but a different crystal structure: pyrite crystallises in the cubic system, marcasite in the orthorhombic system. Compared with pyrite it is paler, more brittle and much less stable in a damp environment; as it decays it forms sulfuric acid. Its name causes confusion: the stones of jewellery sold as “marcasite jewellery” are in fact usually pyrite.
What is marcasite used for?
Marcasite is not an ore or a gemstone in its own right; it belongs in mineral collections and is the source of the name “marcasite jewellery”. Because it is prone to decay, it is kept protected from damp in museums and collections.
How hard is marcasite?
It has a hardness of 6–6.5 on the Mohs scale. It can scratch glass; a steel knife scratches it only with difficulty. Its specific gravity is 4.88–4.89 g/cm³.
Where is marcasite found?
Its best-known localities: Dover, Kent, England; Freiberg, Saxony, Germany; Joplin, Missouri, USA; Cap Blanc-Nez, Pas-de-Calais, France; Reocín mine, Cantabria, Spain.
Where is marcasite found in Türkiye?
Known localities in Türkiye: Murgul, Artvin, Türkiye; Çayeli (Madenköy), Rize, Türkiye; Karabaşvengi, Divriği, Sivas, Türkiye.
How can you tell if marcasite is real?
A fresh surface is tin-white to pale bronze-yellow; it is less golden than pyrite. It darkens in air and may form an iridescent tarnish. Its hardness is 6–6.5 (the same as pyrite): a steel knife does not scratch it. It is brittle. Its streak (powder colour) is gray or brownish black. The stones in jewellery sold as “marcasite jewellery” are not real marcasite but cut and polished pyrite, because marcasite is very brittle and decays in damp conditions, forming sulfuric acid. The name dates from before the scientific definition.
Is marcasite valuable?
On the “street to diamond” value ladder it sits on step 3 of nine: Building and industrial stone. Marcasite is not valuable as an industrial ore or as a jewellery stone; its tendency to decay limits its uses. For collectors, its worth depends on the form of the crystals (twinned groups such as cockscombs or spearheads), their lustre, freedom from damage and decay, and a famous locality; specimens kept safe from damp hold their value. For pieces sold as “marcasite jewellery”, what counts is not the stone but the metalwork, the age and the condition, because the stone is mostly pyrite.
What is marcasite good for?
Jewellery sellers and crystal-therapy sites associate marcasite with wisdom, courage and self-expression. The same sources say marcasite lends strength to meditation and increases creativity in the arts. There is no scientific evidence that marcasite gives wisdom, courage or creativity. Because the stones of “marcasite” jewellery are mostly pyrite, these claims are often really made for pyrite too. Real marcasite decays in damp conditions, forming sulfuric acid: it should not be put in water to make “gem water” or an “elixir”, and should not be put in the mouth. This section reports beliefs; it is not health information. There is no scientific evidence for these claims and no stone replaces medical treatment.
Is marcasite dangerous?
Marcasite is an iron sulfide. Handling it is generally harmless. In damp conditions, however, it decays much faster than pyrite: iron sulfate and sulfuric acid form, and the acid corrodes labels, boxes and nearby sulfide specimens (“pyrite decay”). Do not touch a specimen coated with a whitish-greenish crust with bare hands; store marcasite specimens somewhere dry, below 60 per cent humidity. Do not heat it; irritating sulfur dioxide gas is released. Do not put it in your mouth, and do not put it in water to make “gem water” or an “elixir”: acid forms as it decays.
Sources
- Handbook of Mineralogy: Marcasite · Mineralogical Society of America
- Marcasite · Wikipedia
- Marcasite jewellery · Wikipedia
- Marcasite · Encyclopaedia Britannica
- Çakmakkaya ve Damarköy (Murgul-Artvin) Bakır Yataklarında Sıvı Kapanım, Oksijen ve Hidrojen İzotopları Jeokimyası İncelemeleri (A. Gökçe) · Türkiye Jeoloji Bülteni 44(2), 2001
- Rize-Çayeli-Madenköy Bakır-Çinko-Kurşun Kompleks Sülfürlü Cevherinin Flotasyonla Zenginleştirilmesinde Yeni Bir Yöntem: SO2-Sıcak Flotasyon (H. Uzun, B. Çevirmen) · Maden Mühendisleri Odası arşivi (maden.org.tr)
- Murmano Granitoidi'nin (Divriği-Sivas) Kuzeyindeki Karabaşvengi Demir Cevherleşmesi ve Divriği Demir Yataklarının Kökeninin İrdelenmesi (A. R. Çolakoğlu, T. Arıkal, U. Akın) · 56. Türkiye Jeoloji Kurultayı bildiri özü (Maden Yatakları oturumu)
- Joplin, Missouri · Wikipedia
- Cap Blanc-Nez · Wikipedia
- Dover · Wikipedia
- Reocín · Wikipedia
- Freiberg · Wikipedia
- Santa Eulalia, Chihuahua · Wikipedia
- Llallagua · Wikipedia
- Murgul · Wikipedia
- Divriği · Wikipedia
External links
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