Template:Short description Template:Infobox mineral
Murdochite is a mineral combining lead and copper oxides with the chemical formula Template:Chem (x ≤ 0.5).<ref>http://rruff.geo.arizona.edu/doclib/hom/murdochite.pdf Handbook of Mineralogy</ref>
It was first discovered in 1953 in the Mammoth-Saint Anthony Mine in Pinal County, Arizona by Percy W. Porter, a mining engineer who handpicked a 401.5-mg sample.<ref name=Fahey>Fahey, Josepf J., (1955) Murdochite, A new Copper Lead Oxide Mineral. American Mineralogist 40, 905–906.</ref> Porter would later submit for analysis and it was then that Fred A. Hildebrand suggested that the sample was a new mineral after taking a powder x-ray picture.<ref name=Fahey/> It was named for Joseph Murdoch (1890–1973), American mineralogist.<ref>http://www.mindat.org/min-2812.html Mindat.org</ref> Murdochite was first suggested to be of a cubic structure.<ref name=Christ>Christ, C. L., and Clark, Joan R. (1955) The Crystal Structure of Murdochite. American Mineralogist 40, 907–916.</ref> After this suggestion, the term "murdochite-type structure" began to be used when describing a structure that is similar to that of murdochite.<ref name=Winkler>Winkler, Björn, Chall, Michael, Pickard, Chris J., Milman, Victor, and White, Jim. (2000)Structure of Cu6PbO8. Acta Crystallographica 56, 22–26.</ref> Murdochite was later found to be octahedral.<ref name=Dubler>Dubler, Erich, Vadani, Angelo, and Oswald, Rudolf Hans. (1983) New Structure Determination of Murdochite, Cu6PbO8. Acta Crystallographica 39, 1143–1146.</ref>
CompositionEdit
Various studies have examined the composition of murdochite. When murdochite was first discovered, its chemical formula was determined through stoichiometry to be Cu6·1Pb0·9O8·O.<ref name=Fahey/> The ideal formula for murdochite was originally thought to be Template:Chem2.<ref name=Christ/> This formula failed to take into consideration the significant amounts of chlorine and bromine present in murdochite. Using electron microprobe analysis, a new chemical composition for murdochite was determined that included chlorine and bromine. This new formula was Template:Chem and was created with regard to the Cu/Pb variance observed in samples of murdochite from both Hansonburg, New Mexico, and T. Khuni mine, Iran.<ref name=Burke>Burke, E. A. J., and Maaskant, P. (1970) New Data on Murdochite. Nues Jahrb. Mineral Montlsh. 558–565.).</ref> This new composition was also proven incorrect and the formula that is widely accepted today, Template:Chem (x ≤ 0.5), was proposed.<ref name=Dubler/>
StructureEdit
The structure originally proposed for murdochite was a simple cubic structure.<ref name=Adib/> This structure was later proven incorrect and determined to be octahedral.<ref name=Dubler/> The structure of murdochite is described as edges of [PbO8] cubes spanned by Cu2+ ions that give a square-planar CuO4 arrangement in a three-dimensional network.<ref name=Dubler/> Halogen ions complete a (4 + 2_ elongated Template:Chem2 octahedron.<ref name=Dubler/>
Physical propertiesEdit
Murdochite is an opaque mineral that exhibits a black color, adamantine luster, black streak, and isotropic optical class.<ref name=Anthony>Anthony, J.W., Bideaux, R., Bladh, K. and Nichols, M. (2003) Murdochite Template:Chem (x < 0.5). Handbook of Mineralogy. Mineral Data Publishing (Republished by the Mineralogical Society of America).</ref> Samples from T. Khuni mine indicate that polished sections of murdochite resemble the color and reflectivity of magnetite but vary because of zoning.<ref name=Adib>Adib, D., and Ottermann, J. (1970) Some New Lead Oxide Minerals and Murdochite from T. Khuni Mine, Anarak, Iran. Mineralium Deposita 5, 1, 86–93.</ref> The lighter zones in murdochite are caused because they are richer in lead than the darker zones.<ref name=Adib/> The mineral is known to be brittle, have a hardness of 4, and have {111} cleavage.<ref name=Anthony/> Murdochite also has a pink tinge that is distinctive and its edges seem to be more reflective than the center because samples are commonly porous in the center and compact on the sides with clean-cut faces.<ref name=Adib/> The space group of murdochite has been confirmed to be Fm3m.<ref name=Christ/><ref name=Dubler/> Murdochite can be cubic, with a point group of 4/m 3 2/m, or octahedral and cubo-octahedral whose point group is 2 mm.<ref name=Anthony/> Murdochite can occur in the forms (100) and (111) with crystal twinning being very common.<ref name=Adib/> The calculated density of murdochite was determined to be 6.1 g/cm3 and have a measured density of 6.47 g/cm3.<ref name=Fahey/><ref name=Christ/>
Geologic occurrenceEdit
Naturally occurring murdochite, Template:Chem (x ≤ 0.5), was discovered in Mammoth Mine, Arizona.<ref name=Fahey/> The mine, about 46 miles northeast of Tucson, contains deposits of molybdenum, lead, gold, zinc, vanadium, sphalerite, and galena.<ref name=Fahey/> In this mine, murdochite was found embedded in plates of wulfenite as well as on the surface of crystals of fluorite.<ref name=Fahey/> Other crystals found in Mammoth Mine include hemimorphite, willemite, and quartz.<ref name=Fahey/> Larger masses of murdochite have also been found at the T. Kguni Mine in Anarak, Iran.<ref name=Adib/> Here murdochite was found in conjunction with khuniite (iranite), chrominium (phoenicochroite), plumangite and an unknown mineral with the formula Pb9O16.<ref name=Adib/> All these minerals are lead oxide minerals, meaning that murdochite can be found in oxidized Pb-Cu deposits.<ref name=Anthony/> More recently, small murdochite crystals were found encrusting aurichalcite crystals in the Granite Gap Mines in New Mexico.<ref name=Beyer>Beyer, Joan. (2002) Minerals of the Granite Gap Mines. Rocks & Minerals 77, 5, 298–305.</ref>
Origin of the nameEdit
The mineral murdochite is named after Joseph Murdoch, who was once a professor of geology at the University of California, Los Angeles and a past president of the Mineralogical Society of America.<ref name=Webb>Webb, Robert W. (1975) Memorial of Joseph Murdoch February 19, 1890 – December 31, 1973. American Mineralogist 60, 511–513.</ref> Professor Murdoch was born February 19, 1890, and died December 31, 1973, at 83 years of age.<ref name=Anthony/> Murdoch obtained a baccalaureate degree, an M.S. and a Ph.D. in geologic science by 1915 from Harvard University and would first be involved in a non-geological business career before joining the faculty at the department of geology at the University of California, Los Angeles in 1928.<ref name=Webb/> It was here that Murdoch returned to work in the geologic field that would lead to the publishing of numerous papers which would include 23 publications ranging from the years 1913–1968, along with ten published abstracts and many book reviews.<ref name=Webb/>