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Dawsonite

Abstract

Dawsonite is a relatively rare, hydrothermal, anhydrous carbonate mineral that crystalizes at low-­‐temperature conditions and normal atmospheric pressures when minum silicates decompose in contact with carbonate/bicarbonate rich solutions. Dawsonite has only been found in seven localities in the world, from encrusting vug walls in hydrothermally altered feldspathic dikes, to it’s authigenic state in shales and coal beds in the Green River Formation in Colorado (Smith and Milton, 1966). The name honors John William (J.W.) Dawson, a Canadian geologist and principal of McGill University the university’s campus in 1874.

Introduction

Dawsonite is a sodium aluminum hydroxy carbonate (NaAlCO3 (OH)2) that is generally linked to fluid inclusions and crystalized melt inclusions consisting of mica, Calcium sulfate, and Aluminum-rich silicates (Sirbescu and Nabelek, 2003). Dawsonite's origin was initially believed to be an alteration product of alkali feldspars in certain hydrothermal environments (Goldbery and Loughnan, 1972). For now, dawsonite's importance likes with pharmaceuticals as an antacid. However, its potential as a possible ore for aluminum could make dawsonite a much more sought after mineral. Researchers estimate that one square mile of dawsonite deposits could yield more aluminum than the total reserves of bauxite available in the United States (Goldbery and Loughnan, 1972).

Composition

The chemical formula of Dawsonite is MAl(CO3)(OH)2, where M can represent Na-D, K-D, or NH4-D meaning sodium dawsonite, potassium dawsonite, and ammonium dawsonite. The primary form found is sodium dawsonite, which completely decomposes in a reaction with warm (0.5 N) hydrochloric ccid, yielding 2.91% CO2. This reaction also revealed 1.59% Na2O, 2.27% Al2O3, 0.52% CaO, 0.44% MgO, and 0.49% FeO. In a seperate experiment, heating the mineral at 5°C per minute to a range of 290-330°C also completely decomposes the mineral, and results in a 2.15% weight loss. The chemical composition in weight percent oxides is primarily comprised of aluminum oxide and carbon dioxide, and trace elements of potassium, iron, and titanium.

Geologic Occurrence

Dawsonite, first discovered in 1874, was found coating vug walls and fractures in hydrothermally altered feldspathic dikes and hornfels associated with nepheline syenite in Mont Saint-Bruno, Canada on the McGill University campus. It has since been found in several localities across the world, most significantly in oil shales and siliciclastic sedimentary rocks permeated by magmatic CO2 in the Green River Formation of Colorado, USA (Smith and Wilton, 1966). Dawsonite does not have a specific mineral that it is associated with at every locality it is found. For example, in the Singleton Coal Measures of the Sydney Dawsonite Basin, dawsonite is found near kaolinite, illite, and expandable lattice clay minerals and in the Green River Formation it is found in dolomite (Smith and Milton, 1966). In the Olduvai Gorge region of Tanzania, dawsonite is found in altered Pleistocene ash deposits and in the Sydney Basin it was first recorded forming cement in lithic sandstones (Loughnan and See, 1967). The Singleton Coal Measures have produced dawsonite as an alteration product of feldspars and quartz, as an interstitial cement in sandstones and conglomerates, as joint and fissure in-fillings in clastics, and predominantly as facings in cleats and other micro fractures in coal (Loughnan and Goldbery, 1972). Although dawsonite is not commonly associated with other minerals, its closest companion is nordstrandite (Al(OH)3) in sandstones, but nordstrandite is not normally detected by X-ray diffraction; meaning that it rarely comprises more than 1-2% of any shared rock (Loughnan and Goldbery, 1972). In the Permian Berry formation of the Sydney Basin, the fact that nordstrandite forms around the rim of dawsonite crystals, leads mineralogists to believe that it is a secondary product of dawsonite formation (Goldbery and Loughnan, 1970).

Atomic Structure

X-ray spectroscopy research of dawsonite has been relatively scarce, but X-ray crystallography has suggested that dawsonite has a regular structure with no complexities. However, a rotationof the structure reveals that the mineral has a hole in its structure, revealing a hidden complexity in each spectral region. It is possible that this hole might be used to trap heavy metals. Analyzing the structure indicates that the (CO3)²^- ion is not involved in bonding due to symmetry reduction. Also in the X-ray crystallography structure, all OH units are equivalent and the estimated distance between the OH units is between 0.2735 and 0.27219, resulting in strong hydrogen bonding (Frost and Bouzaid, 2007).

Physical Properties

Sirbescu and Nabelek (2003) observed dawsonite in the Tin Mountain pegmatite of the Black Hills and discovered short prismatic, rhombic, or pseudo-cubic crystals. As opposed to the shard (hair-life) crystals normally found in inclusions of hydrothermal quartz; crystal sizes range from 3-50 micrometers. They also observed that in plane-polarized light, the mineral's refractive index varies, which is consistent with dawsonite's high bi-refringence of 0.127. in the Singleton Coal Measures, Loughnan and Goldbery observed that dawsonite's most prevalent form was as facings and encrustations along the cleats in the coal and also in sedimentary joint fillings and other sedimentary fissures (Loughnan and Goldbery, 1972). Dawsonite's crystal system is orthorhombic di-pyrimidal and its point group s 2/m 2/m 2/m and its space group is 1mam resulting in a morphology of bladed acicular crystals forming incrustations and rosettes. The Na ions are in four-fold coordinated with the O2 ions. Dawsonite's cleavage is perfect in the (110) plane, has a Mohl's hardness of 3, and its density is measured at 2.436. The mineral is usually colorless to white, has a white streak, has a vitreous luster that gives it a transparent appearance and effervesces with cold HCL.

Biographical Sketch

Dawsonite was named after Sir John William (J.W.) Dawson, a Canadian geologist who served as principal of McGill University where the mineral was first found during the construction of the university's Redpath Museum. In 1865, Dawson published a paper describing the first fossil plants found in Devonian age rocks; this seminal publishing has earned him the title as one of the founding fathers of Paleobotany. However, Dawson's namesake is usually associated with his 1865 study of Eozoon canadense. Found in the Laurentian rocks, Dawson describes the organismas having the structure of a foraminifer, making it the oldest known fossil (London and Edinburgh, 1901).

Literature Search

The most highly cited paper on Web of Science was Frost and Bouzaid's "Raman Spectroscopy of Dawsonite NaAl(CO3)(OH)2" (2007) with 49 citations. The second most cited paper regarding Dawsonite was Smith and Milton's "Dawsonite in Green River Formation of Colorado" (1966). Frost and Bouzaid's research was based around the Raman Spectroscopy of Dawsonite at two different temperatures, 298 K and 77K. Complemented with infrared spectroscopy, Frost and Bouzaid studied the crystal structure of Dawsonite to attempt to disprove the misconception that the mineral's structure was simple (Frost and Bouzaid, 2007). In the Green River Formation of Colorado, Smith and Milton studied Dawsonite in oil shales of the Piceance Basin and in Pleistocene ash beds. Smith and Milton's research reveals that in the Green River Formation, Dawsonite forms as a reaction of carbonate solutions with the silicate mineral, Nepheline. Unlike it's other ocurrences where Dawsonite has been linked to hydrothermal activity, volcanic episodes, and a reaction with varying ore mineralization (Smith and Milton, 1966).

References

• Benezeth, Pascale, et al (2007) Dawsonite Synthesis and Reevaluation of Its Thermodynamic Properties from Solubility Measurements: Implications for Mineral Trapping of CO(2) Geochimica Et Cosmochimica Acta 71.18. 4438-4455

• (Corazza, E., C. Sabelli, and S. Vannucci (1977) Dawsonite: new mineralogical data and structure refinement. Neues Jahrb. Mineral. Monatsh., 381–397.

• Coveney, R.M., W. C. Kelly (1971) Dawsonite as a Daughter Mineral in Hydrothermal Fluid Inclusions. Contributions to Mineralogy and Petrology 32.4. 334

• Frost, R.L., Bouzaid, J.M. (2007) Raman Spectroscopy of Dawsonite Naal(Co3)(Oh)(2) Journal of Raman Spectroscopy 38.7 873-879

• Goldbery, R., Loughnan, F.C. (1970) Dawsonite and Nordstrandite in Permian Berry Formation of Sydney-Basin, New-South-Wales. American Mineralogist 55.3-55.4. 477

• Hay, R. L. (1963) Zeolitic weathering in Olduvai Gorge, Tanzania. Geol. Soc. Amer. Bull. 74, 128l-1286.

• Harrington (1874) Canadian Naturalist and Quarterly Journal of Science: 7: 305.

• London and Edinburgh (1901) Being Autobiographical Notes By Sir William Dawson, Fifty Years of Work in Canada.

• Loughnan, F. C., R. Goldbery (1972) Dawsonite and Analcite in Singleton Coal Measures of Sydney Basin. American Mineralogist 57.9-57.10. 1437

• Loughnan, F.C. (1967) Dawsonite in Greta Coal Measures at Muswellbrook, New South Wales. American Mineralogist 52. 7-8. 1216

• Palache, C., H. Berman and C. Frondell (1960) The System of Mineralogy…of Dana 7th ed., John Wiley & Sons, New York 1124 pp.

• Sirbescu, Mona-Liza C., Nabelek, P. I. (2003) An Inclusion Mineral in quartz from the Tin Mountain pegmatite, Black Hills, South Dakota. Amer. Mineral. 88.1055-1066

• Smith, J. W., Milton, C. (1966) Dawsonite in Green River Formation of Colorado. Economic Geology 61.6.1029

• Worden, R. H. (2006) Dawsonite Cement in the Triassic Lam Formation, Shabwa Basin, Yemen: A Natural Analogue for a Potential Mineral Product of Subsurface CO2 Storage for Greenhouse Gas Reduction. Marine and Petroleum Geology 23.1. 61-77

• Zhang, X. F., et al. (2004) Hydrothermal Synthesis and Thermodynamic Analysis of Dawsonite-Type Compounds. Journal of Solid State Chemistry 177.3. 849-55

• http://www.mindat.org/min-1240.html

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