Chrisstanleyite
Encyclopedia
Chrisstanleyite, Ag2Pd3Se4, is a selenide mineral that crystallizes in high saline, acidic hydrothermal solution at low temperatures as part of selenide vein inclusions in and alongside calcite
veins. It tends be found in assemblages of other selenides: jagueite, naumannite, fischesserite, oosterboschite, and tiemannite, and it is a solid solution
mineral with jagueite Cu2Pd3Se4 in which it shares a unique crystal structure
that has not been identified elsewhere (Paar et al. 1998; Nickel 2002; Paar et al. 2004). Chrisstanleyite and jagueite are unlike the other minerals of the selenide family as they do not have a sulfide
analogue (Topa et al. 2006). First discovered by Dr. Werner Paar from a sample received from Hope’s Nose, Torquay, Devon, England, chrisstanleyite has since been discovered in the Pilbara region of Western Australia and in El Chire, La Rioja, Argentina. Chrisstanleyite was named after the Deputy Head and Associate Keeper at the Department of Mineralogy at The Natural History Museum
in London, Dr. Chris Stanley, for his work and contributions in ore mineralogy (Paar et al. 1998), which include identifying over 40 minerals and writing over 100 peer reviewed articles.
analyses.The results of the analysis allowed Paar et al. (1998) to derive the average composition as (Ag2.01Cu0.02)Σ2.03Pd3.02Se3.95, or the ideal formula of Ag2Pd3Se4. The weight percent per element to create the ideal formula is Pd 37.52, Ag 25.36, Se 37.12, totaling 100% (Paar et al. 1998).
The presence of Cu in the sample proved important as the discovery of chrisstanleyite in the Pilbara Region of Western Australia found intergrown with an unnamed Cu-dominant equivalent (Nickel 2002). In 2004, this unknown mineral was officially named jagueite, Cu2Pd3Se4, after being found in El Chire, Argentina (Paar et al. 2004) and has been identified to form a solid-solution with chrisstanleyite (Paar et al. 1998; Nickel 2002; Paar et al. 2004).
in and along calcite veins that cut through limestone
(Paar et al. 2004). A selenide vein 10cm below a calcite vein in Hope’s Nose, where chrisstanleyite was initially identified, reflected a well-defined zoned sequence of minerals. The top of the sequence included native gold with small amounts of silver, while the middle layer consisted of palladian gold. The bottom layer consisted of selenide mineralization
, primarily made of fischesserite (Paar et al. 1998).
Chrisstanleyite was identified in a second deposit, a dolomite
-rich assemblage in the Pilbara region of Western Australia. Within the assemblage included a homogeneous fine-grained layer of malachite
, quartz
, and goethite
along with heterogeneous grouping of dark nodules and masses in a malachite-quartz matrix. A group of selenides were found in these masses and include berzelianite Cu2Se, umangite
Cu3S2, naumannite Ag2Se, oosterboschite (Pd, Cu)7Se5, luberoite Pt5Se4, chrisstanleyite, and, at the time, the unknown jagueite (Nickel 2002; Paar et al. 2004). Native silver, gold, unidentified palladium and platinum oxides, and several other minerals were identified as well. A similar ore deposit was found in Northern Australia and had had microthermometry and low-temperature laser Raman spectroscopy
utilized in this assemblage. The results showed the minerals came from an acidic, high saline hydrothermal solution at temperatures of 140°C. The interaction of hydrothermal fluids with feldspathic rocks precipitated the ore minerals (Nickel 2002).
A third deposit of chrisstanleyite was found in El Chire, La Rioja, Argentina in a cutting calcite vein containing only one selenide-bearing vein through a hematite
-rich sandstone and arkose
host rocks. These rocks, similar to those from the Pilbara Region in Australia, were hydrothermally altered. The selenide vein included similar minerals tiemannite
HgSe, naumannite, clausthalite
, umangite, klockmannite, chrisstanleyite, and jagueite. It was identified that the grains of chrisstanleyite were surrounded by a rim of unnamed platinum-group
metals, which were too thin to extract for identification, though it is associated with a silvery-mercury alloy. This allowed determination of crystallization for the selenide assemblage: chrisstanleyite and jagueite → (clausthalite) → naumannite and tiemannite → umangite and klockmannite → Pd-free native gold (Paar et al. 2004).
, resulting in the corrugation of the silver-based layer as well the sharing of Se atoms with Pd polyhedra (Topa et al. 2006).
The second framework consists of single coordination squares of Pd1 and paired Pd2 polyhedra, which create a zig-zag composition. These Pd2 polyhedra are layered at an angle (010) and interconnected by the Pd1 squares. This then creates the c glide planes that cause the zig-zag pattern (Topa et al. 2006).
Stability in the two frameworks is created by the metal-metal bonds in the direction of [210]. These interconnect the metal atoms of one [010] layer of the zig-zag structure, as well as taking the Pd2 arrangement of both adjacent layers. The linear arrangement of these three layers creates stability for the creased angles of the Pd2 zig-zag pattern (Topa et al. 2006).
The structures found in chrisstanleyite and jagueite appear to be different than that of any other mineral. Comparing these with other Pd and Pt sulfides and selenides, no relations have been found. The closest structure found was with KCuPdSe5, which also forms corrugated layers, but the diagonally stacked squares are only one polyhedron deep. Additionally, the distances of Pd-Cu structures are not that of metal-metal bonds. Topa et al. (2006) concluded that chrisstanleyite and jagueite are a new structure type lacking a sulfide counterpart.
. The difference between the two is that chrisstanleyite anisotropic rotation tints is much more colorful (Paar et al. 1998). Chrisstanleyite, also, forms a limited solid-solution with jagueite (Nickel 2002; Paar et al. 2004). Based on samples found in the Pilbara Region, the two minerals were both yellow and indistinguishable in reflected light and had weak bireflectance and moderate anisotropy (Nickel 2002).
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:...
veins. It tends be found in assemblages of other selenides: jagueite, naumannite, fischesserite, oosterboschite, and tiemannite, and it is a solid solution
Solid solution
A solid solution is a solid-state solution of one or more solutes in a solvent. Such a mixture is considered a solution rather than a compound when the crystal structure of the solvent remains unchanged by addition of the solutes, and when the mixture remains in a single homogeneous phase...
mineral with jagueite Cu2Pd3Se4 in which it shares a unique 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...
that has not been identified elsewhere (Paar et al. 1998; Nickel 2002; Paar et al. 2004). Chrisstanleyite and jagueite are unlike the other minerals of the selenide family as they do not have a sulfide
Sulfide
A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...
analogue (Topa et al. 2006). First discovered by Dr. Werner Paar from a sample received from Hope’s Nose, Torquay, Devon, England, chrisstanleyite has since been discovered in the Pilbara region of Western Australia and in El Chire, La Rioja, Argentina. Chrisstanleyite was named after the Deputy Head and Associate Keeper at the Department of Mineralogy at The Natural History Museum
Natural History Museum
The Natural History Museum is one of three large museums on Exhibition Road, South Kensington, London, England . Its main frontage is on Cromwell Road...
in London, Dr. Chris Stanley, for his work and contributions in ore mineralogy (Paar et al. 1998), which include identifying over 40 minerals and writing over 100 peer reviewed articles.
Composition
The chemical formula of chrisstanleyite is Ag2Pd3Se4 and contains trace amounts of Cu (Paar et al. 1998). Based on the sample received from Hope’s Nose, England, Paar (1998) was able to utilize 7 grains in two polished sections to run 26 electron-microprobeElectron 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...
analyses.The results of the analysis allowed Paar et al. (1998) to derive the average composition as (Ag2.01Cu0.02)Σ2.03Pd3.02Se3.95, or the ideal formula of Ag2Pd3Se4. The weight percent per element to create the ideal formula is Pd 37.52, Ag 25.36, Se 37.12, totaling 100% (Paar et al. 1998).
The presence of Cu in the sample proved important as the discovery of chrisstanleyite in the Pilbara Region of Western Australia found intergrown with an unnamed Cu-dominant equivalent (Nickel 2002). In 2004, this unknown mineral was officially named jagueite, Cu2Pd3Se4, after being found in El Chire, Argentina (Paar et al. 2004) and has been identified to form a solid-solution with chrisstanleyite (Paar et al. 1998; Nickel 2002; Paar et al. 2004).
Geologic Occurrence
Chrisstanleyite occurs in selenide inclusionsInclusions
Inclusions are non-living substances that may or may not be present in a cell, depending on the cell type. Inclusions are stored nutrients, secretory products, and pigment granules...
in and along calcite veins that cut through limestone
Limestone
Limestone is a sedimentary rock composed largely of the minerals calcite and aragonite, which are different crystal forms of calcium carbonate . Many limestones are composed from skeletal fragments of marine organisms such as coral or foraminifera....
(Paar et al. 2004). A selenide vein 10cm below a calcite vein in Hope’s Nose, where chrisstanleyite was initially identified, reflected a well-defined zoned sequence of minerals. The top of the sequence included native gold with small amounts of silver, while the middle layer consisted of palladian gold. The bottom layer consisted of selenide mineralization
Mineralization (geology)
In geology, mineralization is the hydrothermal deposition of economically important metals in the formation of ore bodies or "lodes".The first scientific studies of this process took place in Cornwall, United Kingdom by J.W.Henwood FRS and later by R.W...
, primarily made of fischesserite (Paar et al. 1998).
Chrisstanleyite was identified in a second deposit, a dolomite
Dolomite
Dolomite is a carbonate mineral composed of calcium magnesium carbonate CaMg2. The term is also used to describe the sedimentary carbonate rock dolostone....
-rich assemblage in the Pilbara region of Western Australia. Within the assemblage included a homogeneous fine-grained layer of malachite
Malachite
Malachite is a copper carbonate mineral, with the formula Cu2CO32. This green-colored mineral crystallizes in the monoclinic crystal system, and most often forms botryoidal, fibrous, or stalagmitic masses. Individual crystals are rare but do occur as slender to acicular prisms...
, quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
, and goethite
Goethite
Goethite , named after the German polymath Johann Wolfgang von Goethe, is an iron bearing oxide mineral found in soil and other low-temperature environments. Goethite has been well known since prehistoric times for its use as a pigment. Evidence has been found of its use in paint pigment samples...
along with heterogeneous grouping of dark nodules and masses in a malachite-quartz matrix. A group of selenides were found in these masses and include berzelianite Cu2Se, umangite
Umangite
Umangite is a copper selenide mineral, Cu3Se2, discovered in 1891. It occurs only in small grains or fine granular aggregates with other copper minerals of the sulfide group. It has a hardness of 3. It is blue-black to red-violet in color with a black streak. It has a metallic luster.Umangite is...
Cu3S2, naumannite Ag2Se, oosterboschite (Pd, Cu)7Se5, luberoite Pt5Se4, chrisstanleyite, and, at the time, the unknown jagueite (Nickel 2002; Paar et al. 2004). Native silver, gold, unidentified palladium and platinum oxides, and several other minerals were identified as well. A similar ore deposit was found in Northern Australia and had had microthermometry and low-temperature laser Raman spectroscopy
Raman spectroscopy
Raman spectroscopy is a spectroscopic technique used to study vibrational, rotational, and other low-frequency modes in a system.It relies on inelastic scattering, or Raman scattering, of monochromatic light, usually from a laser in the visible, near infrared, or near ultraviolet range...
utilized in this assemblage. The results showed the minerals came from an acidic, high saline hydrothermal solution at temperatures of 140°C. The interaction of hydrothermal fluids with feldspathic rocks precipitated the ore minerals (Nickel 2002).
A third deposit of chrisstanleyite was found in El Chire, La Rioja, Argentina in a cutting calcite vein containing only one selenide-bearing vein through a hematite
Hematite
Hematite, also spelled as haematite, is the mineral form of iron oxide , one of several iron oxides. Hematite crystallizes in the rhombohedral system, and it has the same crystal structure as ilmenite and corundum...
-rich sandstone and arkose
Arkose
Arkose is a detrital sedimentary rock, specifically a type of sandstone containing at least 25% feldspar. Arkosic sand is sand that is similarly rich in feldspar, and thus the potential precursor of arkose....
host rocks. These rocks, similar to those from the Pilbara Region in Australia, were hydrothermally altered. The selenide vein included similar minerals tiemannite
Tiemannite
Tiemannite is a mineral, mercury selenide, formula HgSe. It occurs in hydrothermal veins associated with other selenides, or other mercury minerals such as cinnabar, and often with calcite. Discovered in 1855 in Germany, it is named after C. W...
HgSe, naumannite, clausthalite
Clausthalite
Clausthalite is a lead selenide mineral, PbSe. It forms a solid solution series with galena PbS.-Occurrence:It occurs in low-sulfur hydrothermal deposits with other selenides and in mercury deposits...
, umangite, klockmannite, chrisstanleyite, and jagueite. It was identified that the grains of chrisstanleyite were surrounded by a rim of unnamed platinum-group
Platinum group
The platinum group metals is a term used sometimes to collectively refer to six metallic elements clustered together in the periodic table.These elements are all transition metals, lying in the d-block .The six...
metals, which were too thin to extract for identification, though it is associated with a silvery-mercury alloy. This allowed determination of crystallization for the selenide assemblage: chrisstanleyite and jagueite → (clausthalite) → naumannite and tiemannite → umangite and klockmannite → Pd-free native gold (Paar et al. 2004).
Structure
The crystal structure for chrisstanleyite has two different polyhedra structures that intersect and support each other, which is the same as jagueite. An AgSe4 (or CuSe4) tetrahedral creates a grooved (100) layer that are grouped in dimers of Ag2Se6, which share four vertices with adjacent dimers. Oriented alternatively above and below the layer are the two remaining vertices for each tetrahedronTetrahedron
In geometry, a tetrahedron is a polyhedron composed of four triangular faces, three of which meet at each vertex. A regular tetrahedron is one in which the four triangles are regular, or "equilateral", and is one of the Platonic solids...
, resulting in the corrugation of the silver-based layer as well the sharing of Se atoms with Pd polyhedra (Topa et al. 2006).
The second framework consists of single coordination squares of Pd1 and paired Pd2 polyhedra, which create a zig-zag composition. These Pd2 polyhedra are layered at an angle (010) and interconnected by the Pd1 squares. This then creates the c glide planes that cause the zig-zag pattern (Topa et al. 2006).
Stability in the two frameworks is created by the metal-metal bonds in the direction of [210]. These interconnect the metal atoms of one [010] layer of the zig-zag structure, as well as taking the Pd2 arrangement of both adjacent layers. The linear arrangement of these three layers creates stability for the creased angles of the Pd2 zig-zag pattern (Topa et al. 2006).
The structures found in chrisstanleyite and jagueite appear to be different than that of any other mineral. Comparing these with other Pd and Pt sulfides and selenides, no relations have been found. The closest structure found was with KCuPdSe5, which also forms corrugated layers, but the diagonally stacked squares are only one polyhedron deep. Additionally, the distances of Pd-Cu structures are not that of metal-metal bonds. Topa et al. (2006) concluded that chrisstanleyite and jagueite are a new structure type lacking a sulfide counterpart.
Special Characteristics
A prominent feature chrisstanleyite has and shares with oosterboschite is that it has fine polysynthetic and parquet-like twinningCrystal twinning
Crystal twinning occurs when two separate crystals share some of the same crystal lattice points in a symmetrical manner. The result is an intergrowth of two separate crystals in a variety of specific configurations. A twin boundary or composition surface separates the two crystals....
. The difference between the two is that chrisstanleyite anisotropic rotation tints is much more colorful (Paar et al. 1998). Chrisstanleyite, also, forms a limited solid-solution with jagueite (Nickel 2002; Paar et al. 2004). Based on samples found in the Pilbara Region, the two minerals were both yellow and indistinguishable in reflected light and had weak bireflectance and moderate anisotropy (Nickel 2002).