Arthurite
Encyclopedia
Arthurite is a mixture of divalent copper and iron ions in combination with trivalent arsenate
, phosphate
and sulfate
ions with hydrogen and oxygen. Initially discovered by Sir Arthur Russell in 1954 at Hingston Down Consols mine in Calstock, Cornwall, England, arthurite is formed as a resultant mineral in the oxidation region of some copper deposits by the variation of enargite
or arsenopyrite
. The chemical formula of Arthurite is Cu
Fe
23+(As
O
4,P
O
4,S
O
4)2(O
,O
H
)2•4H
2O
.
Arthurite is named after Arthur W. G. Kingsbury, a British mineralogist, and Arthur Russell, 6th Baronet
of Swallowfield
, and a collector of minerals.
(Co), in the case of cobaltarthurite, Manganese
(Mn) replaces Cu in the case of earlshannonite, Iron (Fe) in the case of bendadaite and whitmoreite and Zinc
(Zn) in the case of ojuelaite. Arthurite is the copper-dominant end-member of the Arthurite group.
Table 1. Chemical composition of Arthurite in weight percent oxides
Arthurite crystallizes from an aqueous solution with whichever applicable anions are accessible in the solution. These available anions may be carbonate, arsenate, sulphate and phosphate. Some other minerals belonging to the arthurite group are cobaltarthurite, Co2+Fe3+2(AsO4)2(OH)2•4H2O, whitmoreite Fe2+Fe3+2(PO4)2(OH)2•4H2O, ojuelaite, ZnFe2(AsO4)2(OH)2•4H2O, earlshannonite, (Mn,Fe)Fe2(PO4)2(OH)2•4H2O and bendadaite, Fe2+Fe3+2(AsO4)2(OH)2•4H2O. The optimal compositions of the members of the arthurite group can be represented by A2+Fe3+2(XO4)2(OH)2•4H2O and are summarized in Table 2.
Table 2. Compositional breakdown of the arthurite group members
Consols mine in Calstock
, Cornwall
,
England
. A second sample was found in 1966 in the Potrerillos copper deposit, Atacama Province
, northern Chile
. Each of these locations have porphyritic
copper deposits where circulating groundwater interacts with the cooling porphyritic intrusions and their fluids to form copper-bearing minerals and copper ore deposits. The copper ore found at the Chilean site was comprised mainly of massive djurleite
deposits that strongly oxidized to form goethite
, minor cuprite
and malachite
. The arthurite formed as thin (0.1 – 0.5 mm) and sparsely coated areas growing along the inner walls of minor fractures splitting through malachite-rich encased djurleite forms.
and then studied chemistry at Kings College
, London. During his life he amassed an amazing collection of minerals, many from the collections of others, but also from his own field work. When Sir Arthur died in 1964 his collection of 12,000 mineral specimens went to The Natural History Museum in London with the stipulation that the collection not be dispersed, but remain as a British regional collection.
Arsenate
The arsenate ion is AsO43−.An arsenate is any compound that contains this ion. Arsenates are salts or esters of arsenic acid.The arsenic atom in arsenate has a valency of 5 and is also known as pentavalent arsenic or As[V]....
, phosphate
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
and sulfate
Sulfate
In inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...
ions with hydrogen and oxygen. Initially discovered by Sir Arthur Russell in 1954 at Hingston Down Consols mine in Calstock, Cornwall, England, arthurite is formed as a resultant mineral in the oxidation region of some copper deposits by the variation of enargite
Enargite
Enargite is a copper arsenic sulfosalt mineral with formula: Cu3AsS4. It takes its name from the Greek word enarge, "distinct." Enargite is a steel gray, blackish gray, to violet black mineral with metallic luster. It forms slender orthorhombic prisms as well as massive aggregates...
or arsenopyrite
Arsenopyrite
Arsenopyrite is an iron arsenic sulfide . It is a hard metallic, opaque, steel grey to silver white mineral with a relatively high specific gravity of 6.1. When dissolved in nitric acid, it releases elemental sulfur. When arsenopyrite is heated, it becomes magnetic and gives off toxic fumes...
. The chemical formula of Arthurite is Cu
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
Fe
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...
23+(As
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
4,P
Phosphate
A phosphate, an inorganic chemical, is a salt of phosphoric acid. In organic chemistry, a phosphate, or organophosphate, is an ester of phosphoric acid. Organic phosphates are important in biochemistry and biogeochemistry or ecology. Inorganic phosphates are mined to obtain phosphorus for use in...
O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
4,S
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
4)2(O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
,O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
H
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
)2•4H
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...
2O
Oxygen
Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...
.
Arthurite is named after Arthur W. G. Kingsbury, a British mineralogist, and Arthur Russell, 6th Baronet
Baronet
A baronet or the rare female equivalent, a baronetess , is the holder of a hereditary baronetcy awarded by the British Crown...
of Swallowfield
Swallowfield
Swallowfield is a village and civil parish in the English county of Berkshire. It is situated south of the town of Reading, and north of the county boundary with Hampshire....
, and a collector of minerals.
Introduction
Arthurite was determined to be a uniquely new mineral by R.J. Davis and M.H. Hey in 1964 after its initial discovery. A second specimen was confirmed by A.H Clark and R.H. Sillitoe (1969) from Potrerillos, Atacama Province, Chile in 1969. Subsequently several other arthurite-like minerals have been discovered. There are variations in which the Copper (Cu) ions are replaced with CobaltCobalt
Cobalt is a chemical element with symbol Co and atomic number 27. It is found naturally only in chemically combined form. The free element, produced by reductive smelting, is a hard, lustrous, silver-gray metal....
(Co), in the case of cobaltarthurite, Manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
(Mn) replaces Cu in the case of earlshannonite, Iron (Fe) in the case of bendadaite and whitmoreite and Zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
(Zn) in the case of ojuelaite. Arthurite is the copper-dominant end-member of the Arthurite group.
Composition
The theoretical chemical formula of Arthurite was originally determined to be Cu2Fe4(AsO4)3(O,OH)7•6H2O. The breakdown of the composition of arthurite in weight percent oxides is given in Table 1.Table 1. Chemical composition of Arthurite in weight percent oxides
| Element | Oxide | Theoretical Percentage | Recalculated Percentage |
|---|---|---|---|
| Copper | CuO | 16.00 | 14.5 |
| Iron | Fe2O3 | 32.12 | 30.1 |
| Arsenic | As2O5 | 34.67 | 34.8 |
| Hydrogen | H2O | 17.21 | 20.6 |
| Sum | 96.54 | 100 | |
Arthurite crystallizes from an aqueous solution with whichever applicable anions are accessible in the solution. These available anions may be carbonate, arsenate, sulphate and phosphate. Some other minerals belonging to the arthurite group are cobaltarthurite, Co2+Fe3+2(AsO4)2(OH)2•4H2O, whitmoreite Fe2+Fe3+2(PO4)2(OH)2•4H2O, ojuelaite, ZnFe2(AsO4)2(OH)2•4H2O, earlshannonite, (Mn,Fe)Fe2(PO4)2(OH)2•4H2O and bendadaite, Fe2+Fe3+2(AsO4)2(OH)2•4H2O. The optimal compositions of the members of the arthurite group can be represented by A2+Fe3+2(XO4)2(OH)2•4H2O and are summarized in Table 2.
Table 2. Compositional breakdown of the arthurite group members
| Mineral | A-site | X-site | Reference |
|---|---|---|---|
| arthurite Arthurite Arthurite is a mixture of divalent copper and iron ions in combination with trivalent arsenate, phosphate and sulfate ions with hydrogen and oxygen... |
Cu2+ | As5+ | |
| cobaltarthurite | Co2+ | As5+ | |
| whitmoreite | Fe2+ | As5+ | |
| ojuelaite | Zn2+ | P5+ | |
| earlshannonite | Mn2+, Fe2+ | P5+ | |
| bendadaite | Fe2+ | P5+ |
Structure
Arthurite is of the monoclinic space group: P21/c with a = 10.189(2)Å, b = 9.649(2)Å, c = 5.598(1)Å and β = 92.16(2). The coordination polyhedron of the Cu2+ ion is clearly tetragonally lengthened as compared to whitmoreite with the Phosphorus (P) and Arsenic (As). Figure 1 shows the crystal structure of arthurite.Physical Properties
Table 3. General and Physical Properties of arthurite| Attribute | Data |
|---|---|
| Chemical Formula | CuFe23+(AsO4,PO4,SO4)2(O,OH)2•4H2O |
| Color | Apple-green to bluish green |
| Opacity | Transparent to translucent |
| Habit | Acicular, Prismatic, Spherical |
| Hardness | 3-4 (Mohs Mohs scale of mineral hardness The Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer material. It was created in 1812 by the German geologist and mineralogist Friedrich Mohs and is one of several definitions of hardness in... scale) |
| Luster | Vitreous |
| Optical Class | Biaxial (+), may be biaxial (–) |
| Pleochroism | X = colorless to pale green; Y = gray-green; Z = olive-green |
| Orientation | Y = b; Z ^ c = 10 |
| Absorption | Z > Y > X. α = 1.736 β = 1.767 γ = 1.796 |
| Density | D(meas.) = ~3.2 D(calc.) = 3.29 |
| Space group | P21/c. a = 10.189(2) b = 9.649(2) c = 5.598(1) β = 92.16(2)° Z = 2 |
| 2V calculation | ~90° |
Geologic Occurrence
The first specimen on record was sent to the British Museum of Natural History, Department of Mineralogy by Sir Arthur Russell in 1954. The sample specimen was collected by Sir Russell from Hingston DownHingston Down
Hingston Down is a hill not far from Gunnislake in Cornwall in the United Kingdom.-History:This is possibly the Hingston Down mentioned in the Anglo-Saxon Chronicle which says that in 835 Egbert king of the West Saxons defeated an army of Vikings and Cornish at Hengestdun = "Stallion Hill"...
Consols mine in Calstock
Calstock
Calstock is civil parish and a large village in south east Cornwall, England, United Kingdom, on the border with Devon. The village is situated on the River Tamar south west of Tavistock and north of Plymouth....
, Cornwall
Cornwall
Cornwall is a unitary authority and ceremonial county of England, within the United Kingdom. It is bordered to the north and west by the Celtic Sea, to the south by the English Channel, and to the east by the county of Devon, over the River Tamar. Cornwall has a population of , and covers an area of...
,
England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
. A second sample was found in 1966 in the Potrerillos copper deposit, Atacama Province
Atacama Province, Chile
Atacama Province was one of the administrative divisions of Chile from 1843 to 1974. It was created by law on 31 October 1843.The capital was Copiapó.The first departments were:* Copiapó Department* Freirina Department* Vallenar Department...
, northern Chile
Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...
. Each of these locations have porphyritic
Porphyritic
Porphyritic is an adjective used in geology, specifically for igneous rocks, for a rock that has a distinct difference in the size of the crystals, with at least one group of crystals obviously larger than another group...
copper deposits where circulating groundwater interacts with the cooling porphyritic intrusions and their fluids to form copper-bearing minerals and copper ore deposits. The copper ore found at the Chilean site was comprised mainly of massive djurleite
Djurleite
Djurleite is a copper sulfide mineral of secondary origin with formula Cu31S16 that crystallizes with monoclinic-prismatic symmetry. It is typically massive in form, but does at times develop thin tabular to prismatic crystals. It occurs with other supergene minerals such as chalcocite, covellite...
deposits that strongly oxidized to form 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...
, minor cuprite
Cuprite
Cuprite is an oxide mineral composed of copper oxide Cu2O, and is a minor ore of copper.Its dark crystals with red internal reflections are in the isometric system hexoctahedral class, appearing as cubic, octahedral, or dodecahedral forms, or in combinations. Penetration twins frequently occur...
and 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...
. The arthurite formed as thin (0.1 – 0.5 mm) and sparsely coated areas growing along the inner walls of minor fractures splitting through malachite-rich encased djurleite forms.
Biographic Sketch
Arthurite is named after two people, Arthur William Gerald Kingsbury and Sir Arthur Edward Ian Montagu Russell. Arthur Kingsbury was the son of a farmer in East Meon, Hampshire, England. He attended Bradfield College in Berkshire prior to an apprenticeship at a London law firm. He passed the bar exam in 1929 and became a solicitor at Sherborne and then later Crewkerne in the West of England. He began collecting minerals in 1927. After the war he accepted a position as a research assistant in the mineralogy department of the Oxford University Museum where he added 50 species to the list of minerals known to occur in Great Britain. Sir Arthur Edward Ian Montagu Russell was born in 1878 and became the 6th Baronet of Swallowfield Park Reading when his older brother passed away in 1944. Sir Arthur attended the prestigious Eton CollegeEton College
Eton College, often referred to simply as Eton, is a British independent school for boys aged 13 to 18. It was founded in 1440 by King Henry VI as "The King's College of Our Lady of Eton besides Wyndsor"....
and then studied chemistry at Kings College
King's College London
King's College London is a public research university located in London, United Kingdom and a constituent college of the federal University of London. King's has a claim to being the third oldest university in England, having been founded by King George IV and the Duke of Wellington in 1829, and...
, London. During his life he amassed an amazing collection of minerals, many from the collections of others, but also from his own field work. When Sir Arthur died in 1964 his collection of 12,000 mineral specimens went to The Natural History Museum in London with the stipulation that the collection not be dispersed, but remain as a British regional collection.