Paulingite
Encyclopedia
Paulingite or paulingite-K is a rare zeolite
Zeolite
Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents. The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that...

 mineral that is found in vesicles in the alluvial basaltic rocks from the Columbia River
Columbia River
The Columbia River is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia, Canada, flows northwest and then south into the U.S. state of Washington, then turns west to form most of the border between Washington and the state...

 near Rock Island Dam
Rock Island Dam
Rock Island Dam is a hydroelectric dam on the Columbia River in the U.S. state of Washington. Chelan County Public Utility District's Rock Island Dam and Hydro Project was the first dam to span the Columbia, having been built from 1929 to 1933. It is located near the geographical center of...

, Washington.

Paulingite was named for Linus Carl Pauling (1901–1994), professor of chemistry, California Institute of Technology and accepted by the International Mineralogical Association
International Mineralogical Association
The International Mineralogical Association is an international group of 38 national societies. The goal is to promote the science of mineralogy and to standardize the nomenclature of the 4000 plus known mineral species...

 in 1960.

The early formation in the crystallization sequence and the high water content suggest that paulingite forms from relatively dilute pore fluids. They have a large unit cell of 3.51 nanometres and an isometric crystal system and it is largest known inorganic unit cell apart from protein structures. The paulingite structure can be observed while the remaining water content decomposes. A single crystal X-ray refinement of this chemically different sample material derived three main cation positions, which are inside a so called paulingite or Calcium (Ca), between 8-rings of neighbouring Barium (Ba), and in the centre of the non-planar 8-rings of the -cage Potassium (K).

Introduction

Kamb
Barclay Kamb
Walter Barclay Kamb was a long time professor and researcher at the California Institute of Technology . Professor Kamb was one of the first scientists to journey to the Antarctic to study how the glacier sheets move and operate...

 and Oke in 1960 first described paulingite from vesicles in the Tertiary, augite-bearing-basaltic rocks at the Rock Island dam in Washington, where it is associated with clinoptilolite
Clinoptilolite
Clinoptilolite is a natural zeolite comprising a microporous arrangement of silica and alumina tetrahedra. It has the complex formula: 2-3Al32Si13O36·12. It forms as white to reddish tabular monoclinic tectosilicate crystals with a Mohs hardness of 3.5 to 4 and a specific gravity of 2.1 to 2.2...

 (Na,K,Ca)2-3Al3(Al,Si)2Si13O36•12(H2O), phillipsite
Phillipsite
Phillipsite is a mineral of the zeolite group; a hydrated potassium, calcium and aluminium silicate, approximating to 3Al6Si10O32·12H2O. . The crystals are monoclinic, but only complex cruciform twins are known, these being exactly like twins of harmotome...

 (Ca,Na2,K2)3Al6Si10O32•12H2O, calcite
Calcite
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate . The other polymorphs are the minerals aragonite and vaterite. Aragonite will change to calcite at 380-470°C, and vaterite is even less stable.-Properties:...

 (CaCO3), and pyrite
Pyrite
The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold because of its resemblance to gold...

 (FeS2). Zeolite minerals are crystalline, hydrated aluminosilicate
Aluminosilicate
Aluminosilicate minerals are minerals composed of aluminium, silicon, and oxygen, plus countercations. They are a major component of kaolin and other clay minerals....

 of alkali and alkaline cations with a three-dimensional structure. It is a special group of minerals that is important use to different industries. Due to its special properties like attractive adsorption, cation-exchange, dehydration-rehydration and catalysis properties they are used in the nuclear industry, construction industry, agricultural industry, medical industry, petrochemical industry, space industry and domestic products industry. (Fredrick A. Mumpton, 1998).It is a rare zeolite mineral with a dodecahedron crystal form {110} and has a very large unit cell with a= 3.51 nanometres. The mineral information was described by Kamb and Oke (1960) which has Si/Al ratio of 3.0, a BaO range of 0.5-.4.1% and 18.5% of water content. (Tscherinch and Wise, 1982).

Physical, crystallographic information and structure

Paulingite is a perfect clear rhombic dodecahedron of 0.1 to 1.0 mm in diameter. Their attachment to vesicles causes a hemispherical shape exhibiting 5 to 6 planes of dodecahedral planes. In the vesicular walls, they appear to be dark brown to black. They are actually clear and colorless due to clarity and their attachment to the vesicular wall. The crystal faces are smooth and planar and have a bright vitreous luster. The crystals have no cleavage. Under a binocular microscope, it resembles chips of ice. Lamellae seen optically may indicate twinning. They have a conchoidal fracture. It has a white streak. Rhombic dodecahedron is the dominant crystal form for paulingite. The hardness of paulingite is 5. The size of the paulingite unit cell is outstanding because it is the largest inorganic compounds exceeding most complex, intermetallic compounds. The measured density is 2.085 g/cm3 and calculated density is 2.10 g/cm3. The figure below shows the dodecahedron shape of paulingite mineral.

Viewing under a petrographic microscope
Petrographic microscope
A petrographic microscope is a type of optical microscope used in petrology and optical mineralogy to identify rocks and minerals in thin sections. The microscope is used in optical mineralogy and petrography, a branch of petrology which focuses on detailed descriptions of rocks...

, the crystals contains a scattering of minute bubble-like inclusions. Paulingite is mostly isotropic and in extreme cases that faint, isolated, fuzzy and weak birefringent twinning which is a determining factor for differentiating paulingite from analcite
Analcite
Analcime or analcite is a white, grey, or colourless tectosilicate mineral. Analcime consists of hydrated sodium aluminium silicate in cubic crystalline form. Its chemical formula is NaAlSi2O6·H2O. Minor amounts of potassium and calcium substitute for sodium...

 (NaAlSi2O6•H2O) . The refractive index
Refractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....

 at 230 in sodium vapor light by immersion method is 1.473. Single crystal diffraction study provides information that paulingite is cubic and the cubic length of a0=35.10. It was determined from rotation photograph using copper Ka radiation, nickel filtered, with the film in self-calibrating arrangement. The reflections were indexed with the help of a zero-layer Weissenberg photograph. Reflections of the type hkl for l=0 to l=12 have been examined with equi-inclination weissenberg photographs, and only reflections having h+k+l even are observed, indicating a body-centered lattice. The crystal system is isometric. The space group of the paulingite is Im3m and the point group is 4/m3 2/m. (Kamb and Oke 1960).

Geologic occurrence

Paulingite is usually found in vesicles of basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...

 flows. Because of its rarity, certain chemical factors have to be considered for its formation. The exchangeable cations don’t control the formation of paulingite because variations of localities have different percentages to elements e.g. Riggins zeolites are K rich while Chase Creek is Barium rich. Also the Si/Al ratio doesn’t control the formation because the ratio is controlled by the pH of the solution. They may have formed around hydrated or partially hydrated alkali and alkaline earth cations which act as a template. Relatively low-saline solutions promote paulingite framework. So it occurs in sub-alkaline rocks. There are following localities where paulingite are also found which include Riggins in Idaho country, Ritter in Grant county and Chase creek in British Columbia. In Europe, Paulingite was found among zeolites of the Giants Causeway in Ireland and two zeolite localities near Howeneeg and Vogelsberg. (Tscherinch and Wise, 1982).

Distribution

In the USA, at Rock Island Dam, on the Columbia River, Wenatchee, Douglas Co., Washington; from near Riggins, Idaho Co., Idaho; and at Three Mile Creek, near Ritter, Grant Co., Oregon. On Chase Creek, at the junction with Charcoal Creek, north of Falkland, British Columbia, Canada. Large crystals from the Giant's Causeway and Craigahulliar, Portrush, Co. Antrim, Ireland. At Kladno and Vina•rice, Czech Republic. In the Höwenegg quarry, Hegau, Baden-Württemberg, and in the Ortenberg quarry, Vogelsberg, Hesse, Germany.

Association

Zeolite
Zeolite
Zeolites are microporous, aluminosilicate minerals commonly used as commercial adsorbents. The term zeolite was originally coined in 1756 by Swedish mineralogist Axel Fredrik Cronstedt, who observed that upon rapidly heating the material stilbite, it produced large amounts of steam from water that...

mineral species, pyrite and calcite are the important minerals are usually found in association with paulingite.
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