Clearcreekite is a polymorph

Polymorphism (materials science)

Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements...

 of peterbaylissite. The chemical formula of clearcreekite is Hg¹⁺₃CO₃(OH)∙2H₂O. It has a pale greenish yellow color and streak with tabular subhedral crystals and good cleavage on {001}. It is transparent with vitreous luster and uneven fracture. Its density (calculated from the idealized formula) is 6.96 g/cm³. The mineral is monoclinic with the space group

Space group

In mathematics and geometry, a space group is a symmetry group, usually for three dimensions, that divides space into discrete repeatable domains.In three dimensions, there are 219 unique types, or counted as 230 if chiral copies are considered distinct...

 P2/c. Clearcreekite is an extremely rare mineral from the Clear Creek mercury

Mercury (element)

Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

 mine

Mining

Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...

, New Idria district, San Benito County, California

San Benito County, California

San Benito County is a county located in the Coast Range Mountains of the U.S. state of California, south of San Jose. As of 2010 the population was 55,269. The county seat is Hollister, which includes nearly two-thirds of the county's population. El Camino Real passes through the county and...

. It was probably formed after the alteration of other mercury minerals such as cinnabar

Cinnabar

Cinnabar or cinnabarite , is the common ore of mercury.-Word origin:The name comes from κινναβαρι , a Greek word most likely applied by Theophrastus to several distinct substances...

. The mineral is named after the locality where it was found.

History

In 1959, Mr. Edward H. Oyler found a strange-looking mineral in the Clear Creek mercury mine. More than 30 years passed until edoylerite, named on his honor, was properly described by Erd et al.(1993). For more than 20 years Mr. Oyler collected minerals from the same location; deanesmithite, edgarbaileyrite, hanawaltite, peterbaylissite, szymanskiite, wattersite, and clearcreekite are among the new and unique minerals first collected by Mr. Oyler . Some of the minerals share physical characteristics like color and habit but their crystal structure

Crystal structure

In mineralogy and crystallography, crystal structure is a unique arrangement of atoms or molecules in a crystalline liquid or solid. A crystal structure is composed of a pattern, a set of atoms arranged in a particular way, and a lattice exhibiting long-range order and symmetry...

 is completely different, as shown by X-ray powder diffraction data. Clearcreekite is an extremely rare hydrous mercury carbonate mineral.

Compositon

The chemical formula of clearcreekite is Hg₃¹⁺CO₃(OH)∙2H₂O. It is a polymorph of peterbaylissite. The article about peterbaylissite written by Roberts et al. (1995) describe this mineral as orthorhombic with the point group

Point group

In geometry, a point group is a group of geometric symmetries that keep at least one point fixed. Point groups can exist in a Euclidean space with any dimension, and every point group in dimension d is a subgroup of the orthogonal group O...

 2/m, 2/m, 2/m, meanwhile clearcreekite is monoclinic; 2/m. The chemical composition of clearcreekite was obtained after analyzing one of the crystals: Hg₂O= 84.65%, CO₂= 6.16%, H₂O= 6.3%. The results given by the electron microprobe

Electron microprobe

An electron microprobe , also known as an electron probe microanalyzer or electron micro probe analyzer , is an analytical tool used to non-destructively determine the chemical composition of small volumes of solid materials...

 differ slightly from the percentages calculated using the idealized formula: H₂O= 87.54%, CO₂= 6.16%, H₂O= 6.3%. The only elements observed in the study were mercury

Mercury (element)

Mercury is a chemical element with the symbol Hg and atomic number 80. It is also known as quicksilver or hydrargyrum...

, carbon

Carbon

Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

, and oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

.

Structure

The structures of clearcreekite and peterbaylissite are very different but they still are chemically identical. One unique property about them is that the mercury ion does not occur as the mercury(I) ion Hg₂²⁺, but as an Hg¹⁺ ion in an oxysalt. Clearcreekite and peterbaylissite are classified as pure carbonate-bearing minerals with H₂O and OH. The carbonates consist of one central carbon atom surrounded by three oxygen atoms and the molecule easily adheres to hydrogen

Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

. The structure of clearcreekite presents hydrogen bonding between the carbonate and the hydroxyl

Hydroxyl

A hydroxyl is a chemical group containing an oxygen atom covalently bonded with a hydrogen atom. In inorganic chemistry, the hydroxyl group is known as the hydroxide ion, and scientists and reference works generally use these different terms though they refer to the same chemical structure in...

. The unit cell parameters are: a 6.760(4), b 9.580(4), c 10.931(4) Ǻ (angstroms), β 105.53(5)º, V 682.1(6) Ǻ³(cubic angstroms), a:b:c= 0.7056:1:1.1410. The X-ray powder diffraction pattern is very distinctive and unlike any other mineral.

Physical properties

Only two crystals of clearcreekite have ever been found. The longest of them is only 0.17mm and they exhibit tabular, subhedral habit. Clearcreekite is transparent with a pale greenish yellow color and streak, vitreous luster, good cleavage on {001} and it is brittle with uneven fracture. Since the crystals are too small to perform accurate measurements, the hardness of clearcreekite is estimated to be about 2 (because the crystals are highly sensitive to an electron beam) and its density (calculated from the ideal formula) is 6.96 g/cm³.

Geologic occurrence

Mercury deposits in California are located mainly along the San Andreas Fault

San Andreas Fault

The San Andreas Fault is a continental strike-slip fault that runs a length of roughly through California in the United States. The fault's motion is right-lateral strike-slip...

. The deposits are related to the transition of the North American plate

North American Plate

The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, Bahamas, and parts of Siberia, Japan and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust...

 and the Pacific plate

Pacific Plate

The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate....

 boundary from converging to transform. The serpentinite

Serpentinite

Serpentinite is a rock composed of one or more serpentine group minerals. Minerals in this group are formed by serpentinization, a hydration and metamorphic transformation of ultramafic rock from the Earth's mantle...

from the (previously) overriding plate was replaced by silica-carbonate deposits (including cinnabar and mercury) due to the action of hydrothermal fluids. The sequence of mineral formations given by Dunning et al. (2005) show that the rare mercury minerals, including clearcreekite, are very late precipitates in the sequence. The crystals of clearcreekite were originally found on a silica-carbonate rock near specimens of cinnabar and edoylerite.

Special characteristics

Clearcreekite is an extremely rare mineral found only at the Clear Creek mercury mine, New Idria district, San Benito County, California (longitude: 120º43’58” W and latitude 36º22’59” N). The mineral was named after the locality where it was found. The mine has produced about 29 mercury minerals, most of them unique to this area. In 1853, cinnabar was discovered in the region and extensive mining was conducted at the New Idria district. Today the district and the Clear Creek mine are abandoned.