Hellenica World

Boleite

Boleite was first described in 1891, by Mallard & Cumenge, as an oxychloride mineral with a space group of P m3m. It forms in deep blue cubes, and is still being researched; there have been several adjustments to its chemical compositions, and its crystal structure. There are numerous minerals related to boleite, such as pseudoboleite and cumengite, and these all have the same complex structure (Martens 2003). They all contain bright blue cubic structures of octahedron, and are formed in corroded zones of lead and copper deposits, produced during the reaction of chloride with primary sulphides (Rouse, 1973).
Composition

The chemical formula of Boleite is originally illustrated as Pb26 Ag9 Cu24 Cl62 (OH)481- (Rouse, 1973), but was later revised as KPb26 Ag9 Cu24 Cl62 (OH)48 (Hawthorne et al. 2000). A chemical analysis with an electron microprobe was done on a sample of boleite, and only shows the existence of Pb, Ag, Cu and Cl in its chemical composition. Due to several variations and the instrumental restrictions, oxygen levels were not detected in the microprobe analysis (Hawthorne et al. 2000). Therefore, a more accurate crystal structure analysis was carried out, which found and verified the formula KPb26 Ag9 Cu24 Cl62 (OH)48 to be true. The density of the mineral was calculated to be 5.054 and 5.062g/cm3 (Rouse, 1973).

Atomic Structure

The atomic structure of boleite is formed on a body-centered lattice of lead and silver atoms. The only specification to this is that the three Ag(2) atoms are not a part of the body-centered lattice type. Boleite is an octahedral structure, with lead and silver groupings along the pair of body-centered cubic cells. Its structure is coordinated to the faces and the vertices of the polyhedra and chlorine atoms. Faces and vertices with the chlorine hydroxyl ions coordinate the single lead atoms (Hawthorne et al. 2000). The chlorine atoms are shared with Ag(2)Cl6 and Cu(OH)4Cl2 octahedral anion polyhedra. The copper atoms are therefore connected by shared edges. The structure, in detail, would be described as Ag(1), forming an octahedron in the central atom. The eight Cl(1) atoms are above the faces of each of the six octahedron and the six Cl(3) atoms are across the six octahedral vertices (Fig. 1). In Figure 2, the hydrogen bonding of the boleite structure is illustrated. As this figure indicated, the higher Cu circle has been omitted. The Hydrogen bonds in the H(1), along with the H(2) atoms of the OH group of the Cu ring, have been attached to the Cl atoms. (Rouse, 1973).

Physical Properties

The external property of a boleite crystal structure indicates its cubic shape. It is classified under the isometric crystal class. This crystal is usually formed along the direction (100), or a grouping of (100) and (111) directions (Gossner, 1906). Boleite has a perfect cleavage in the a-axis [100] direction, and has a very dark glossy blue color, with has a hardness of 3 – 3.5, and a light greenish-blue color streak. According to a study by G. Friedel, the structures should be referred to as intergrowths of tetragonal crystals (Gossner, 1906). Twinning is best shown in this mineral by notches along the interpenetrated angles, which results in a crystal habit of pseudocubic penetration twinning along three different angles perpendicular to one another. Boleite has cubes over half an inch on each side, which consist of pseudo-octahedral tetragonal dipyramids. (Weber 1974).

Geologic Occurrence

Boleite was first collected as a very minor ore of silver, copper and lead in Boleo, Mexico(Rouse, 1973). There are many other minerals that were originally discovered in Mexico, like gold, iron, molybdenum, zinc, manganese and arsenic. Typically, what is found native to this region are copper, lead and silver extracted minerals. Mexico’s mines have been the site of many mineral extractions since its early discovery of important copper-rich minerals. Several examples of such minerals include danburite, opal, grossular, apatite, rhodochrosite, topaz and other gemstones (Williams 1981). Baja California, a well-known peninsula on the pacific coast of Mexico, is where Boleo is located. Some of the most significant and rare halide minerals such as boleite, pseudoboleite, atacamite, paratacamite and cumengite, were originally discovered there (Williams 1981). Some minerals relate very closely to boleite in their origins. For example, cumengite is a distinctive mineral, which is formed on the faces of the boleite crystal, as a six pointed, star-shaped pyramidal overgrowths (Hawthorne et al. 2000). Another mineral that cannot be formed without the occurrence of boleite is pseudoboleite.

Biographic Sketch

Boleite was named after its place of discovery, Boleo, Mexico, on the Baja peninsula, in a town named Santa Rosalia, which is also where it is primarily located. In 1868, Jose Rosas discovered several types of pellets, which were sent to be examined and analyzed. It was later found that there was an abundance of various mineral resources in this town (Parker, 1981). During this time, a company called El Boleo, owned and operated by Eisenmann and Valle, had begun to be exporting copper and other minerals from this region to Europe and other countries, which resulted in a gold rush in Mexico(Pirsson,1979). This encounter led the Mexican government to explore the Baja California’s mineral resources even further. From 1890 to 1899, El Boleo was the primary manufacturer of copper in Mexico (Pirsson 1979). The mines in Boleo were originally created for business and profit, but lead to the discovery of many rare minerals, such as boleite.

Literature Search / Prospects for Further Research

The most highly cited paper in the Web of Science was “Raman spectroscopy of the minerals boleite, cumengeite, diaboleite and phosgenite - implications for the analysis of cosmetics of antiquity,” by Frost, Williams and Martens, with twenty-seven citations. This article states that the Raman spectroscopy shows the various types of minerals in a complex structure and its mineral formation usage. There is one other article that would be the next on the high citation list: “Crystal Structure of Boleite” (Rouse 1973). Mallard and Cumenge first described the formula, unit cell, and symmetry of Boleite, after Rouse discovered the mineral. Since then, there have been many modifications on the chemical composition of this mineral. In 1981, Samad et al. did a chemical study on the stabilities of boleite and pseudoboleite, in which it was found that boleite has no thermodynamic constancy at the silver ion activity stage. Since Boleite is a rare mineral, its chemical formula is still being researched and various properties are further being discovered.

References

Gossner, Bernard (1906) “The Crystal form of Boleite”. The American Mineralogist. University of Munich 580-582
Hawthorne, Frank C., Cooper, Mark A. (2000). “Boleite: Resolution of the Formula, KPb26 Ag9 Cu24 Cl62 (OH)48. The Canadian Mineralogist. Vol.38. 801-808.
Martens, W., Williams, P.A., Frost, R.L. (2003) “Raman spectroscopy of the minerals boleite, cumengite, diaboleite and phosgenite – implications for the analysis of cosmetics of a antiquity”. Mineralogical Magazine. V.67: 103-111 <http://gsminmage.highwire.org/cgi/content/abstract/67/1/103>
Parker, Robert L (1981). Rocks and Mineral Deposits W.H. Freeman and Company. San Francisco. 343-422.
Pirsson, Louis V (1964). Rocks and Rock Minerals. John Wiley & Sons, Inc. New York, London. 34-56
Rouse, Roland C. (1973/01) “The Crystal Structure of boleite – A Mineral Containing Silver Atom Clusters”. Journal of solid state chemistry 6(1): 86-92 http://hdl.handle.net/2027.42/33968
Weber, Julius (1974). The formation of Minerals. Van Nostrand Reinhold Company. New York, London. 78-80
Williams, Peter A., Thomas, John H., Humphries, Alun,. Samad, Abdul F (1981) “Chemical Studies on the Stabilities of Boleite and Pseudoboleite”. Mineralogical Magazine v.44: 101-104 http://www.minersoc.org/pages/Archive.htm

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