Carpathite is a very rare hydrocarbon mineral, consisting of exceptionally pure

coronene Coronene (also known as superbenzene and cyclobenzene) is a polycyclic aromatic hydrocarbon (PAH) comprising seven peri-fused benzene rings. Its chemical formula is . It is a yellow material that dissolves in common solvents including benzene, tol ...

(C₂₄H₁₂), a

polycyclic aromatic hydrocarbon A polycyclic aromatic hydrocarbon (PAH) is a class of organic compounds that is composed of multiple aromatic rings. The simplest representative is naphthalene, having two aromatic rings and the three-ring compounds anthracene and phenanthrene. ...

. The name has been spelled karpatite and the mineral was improperly renamed pendletonite.

Discovery

The mineral was first described in 1955 for an occurrence in

Transcarpathian Oblast The Zakarpattia Oblast ( uk, Закарпатська область, Zakarpatska oblast) is an administrative oblast located in western Ukraine, mostly coterminous with the historical region of Carpathian Ruthenia. Its administrative centre is ...

Ukraine Ukraine ( uk, Україна, Ukraïna, ) is a country in Eastern Europe. It is the second-largest European country after Russia, which it borders to the east and northeast. Ukraine covers approximately . Prior to the ongoing Russian inva ...

. It was named for the

Carpathian Mountains The Carpathian Mountains or Carpathians () are a range of mountains forming an arc across Central Europe. Roughly long, it is the third-longest European mountain range after the Urals at and the Scandinavian Mountains at . The range stretche ...

. In 1967, unaware of the earlier description, Joseph Murdoch analyzed and described a specimen from the Picacho Peak area of

San Benito County, California San Benito County (; ''San Benito'', Spanish for " St. Benedict"), officially the County of San Benito, is a county located in the Coast Range Mountains of the U.S. state of California. As of the 2020 census, the population was 64,209. The c ...

and named it "pendletonite".

Structure

Carpathite has the same crystal structure of pure coronene. The molecules are planar and lie in two sets with roughly perpendicular orientations. Molecules in the same set are parallel and partially offset, with planes 0.3463 nm apart. That is slightly larger than the inter-layer distance of

graphite Graphite () is a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on la ...

layers (0.335 nm), and much larger than the C-C bond lengths within the molecule (about 0.14 nm). This "corrugated layer" structure is highly resistant to intercalation, which apparently explains the purity of the mineral.

Occurrence

In the Ukraine discovery location, it occurs at the contact zone of a

diorite Diorite ( ) is an intrusive igneous rock formed by the slow cooling underground of magma (molten rock) that has a moderate content of silica and a relatively low content of alkali metals. It is intermediate in composition between low-sil ...

intrusive into

argillite :''"Argillite" may also refer to Argillite, Kentucky.'' Argillite () is a fine-grained sedimentary rock composed predominantly of indurated clay particles. Argillaceous rocks are basically lithified muds and oozes. They contain variable amounts ...

within cavities, and is associated with

idrialite Idrialite is a rare hydrocarbon mineral with approximate chemical formula C22H14. Idrialite usually occurs as soft orthorhombic crystals, is usually greenish yellow to light brown in color with bluish fluorescence. It is named after Idrija, town i ...

amorphous In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid, glassy solid) is a solid that lacks the long-range order that is characteristic of a crystal. Etymology The term comes from the Greek language, Gr ...

organic material,

calcite Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratc ...

barite Baryte, barite or barytes ( or ) is a mineral consisting of barium sulfate ( Ba S O4). Baryte is generally white or colorless, and is the main source of the element barium. The ''baryte group'' consists of baryte, celestine (strontium sulfate), ...

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical f ...

cinnabar Cinnabar (), or cinnabarite (), from the grc, κιννάβαρι (), is the bright scarlet to brick-red form of mercury(II) sulfide (HgS). It is the most common source ore for refining elemental mercury and is the historic source for the bri ...

, and metacinnabar. It has also been reported in the Presov Region of the

Slovak Republic Slovakia (; sk, Slovensko ), officially the Slovak Republic ( sk, Slovenská republika, links=no ), is a landlocked country in Central Europe. It is bordered by Poland to the north, Ukraine to the east, Hungary to the south, Austria to the ...

and in the

Kamchatka Oblast Kamchatka Oblast (russian: Камча́тская о́бласть, ''Kamchatskaya oblast'') was, until being incorporated into Kamchatka Krai on July 1, 2007, a federal subject of Russia (an oblast). To the north, it bordered Magadan Oblas ...

in Russia. In the

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

location, it occurs in centimeter-size veins, associated (and somewhat contemporaneous) with

and cinnabar, in a silicified matrix. Crystals are up to 10 × 1 × 1 mm. Carbon

isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers ( mass num ...

ratios and the morphology of the deposit indicate that the coronene was produced from organic matter in oceanic sediment, thermally decomposed, purified through

hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...

transportation and chemical reactions, and deposition below 250 °C, after the other minerals in the intrusion.

References

Mineralienatlas
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/ref> Webmineral data
/ref> Handbook of Mineralogy
/ref> Joseph Murdoch and Theodore A. Geissman (1967): "Pendletonite, a new hydrocarbon mineral from California". ''American Mineralogist'', volume 52, issues 5-6, pages 611–616. Quote: "''Mr. Forrest Cureton, who sent in the specimens, has asked that the mineral, if it turned out to be new, be named after Mr. Norman H. Pendleton, of Santa Cruz, California, who was apparently the first to suspect that the crystals were not

valentinite Valentinite is an antimony oxide mineral with formula Sb2 O3. Valentinite crystallizes in the orthorhombic system and typically forms as radiating clusters of euhedral crystals or as fibrous masses. It is colorless to white with occasional shad ...

''" Stephen A. Wise, Robert M. Campbell, W. Raymond West, Milton L. Lee, Keith D. Bartle (1986): "Characterization of polycyclic aromatic hydrocarbon minerals curtisite, idrialite and pendletonite using high-performance liquid chromatography, gas chromatography, mass spectrometry and nuclear magnetic resonance spectroscopy". ''Chemical Geology'', volume 54, issues 3–4, pages 339-357. Takuya Echigo, Mitsuyoshi Kimata, and Teruyuki Maruoka (2007): "Crystal-chemical and carbon-isotopic characteristics of karpatite (C₂₄H₁₂) from the Picacho Peak Area, San Benito County, California: Evidences for the hydrothermal formation". ''American Mineralogist'', volume 92, issues 8-9, pages 1262–1269. Max Blumer (1975): "Curtisite, idrialite and pendletonite, polycyclic aromatic hydrocarbon minerals: Their composition and origin" ''Chemical Geology'', volume 16, issue 4, pages 245-256. {{Commons category, Carpathite, position=left Organic minerals Monoclinic minerals Minerals in space group 14 Minerals described in 1955