Lavendulan
Encyclopedia
Lavendulan is an uncommon copper
arsenate
mineral, known for its characteristic intense electric blue color. It belongs to the lavendulan group, which has four members:
Lemanskiite and lavendulan are dimorphs
; they have the same formula, but different structures. Lemanskiite is tetragonal
, but lavendulan is monoclinic
. Lavendulan has the same structure as sampleite, and the two minerals form a series. It is the calcium
analogue of zdenĕkite, and the arsenate
analogue of sampleite.
Lavendulan was originally named for the lavender color
of the "type"
specimen, which has since been determined to be a mixture with no relationship to modern lavendulan. The mineral which is now called lavendulan is not a lavender blue color, and has no relationship to the “type” material from Annaberg. It often contains potassium
, cobalt
and nickel
as impurities.
. Most references describe the lavendulan unit cell as an orthorhombic cell containing 8 formula units (Z=8) but Mindat.org describes a monoclinic unit cell with the length of the c axis halved, and only 4 formula units per unit cell (Z=4) and space group
P21/n. Unit cell parameters are reported as
, satiny in aggregates, and a light blue streak
. It occurs as thin botryoidal crusts of minute radiating fibers or as thin rectangular, pseudo-orthorhombic plates, with cleavage
in three directions, nearly perfect perpendicular to the b crystal axis, and distinct perpendicular to the a and c axes. Twinning
is common. The mineral is brittle, with an uneven fracture
. It is quite soft, with hardness
2.5, between gypsum
and calcite
, and relatively dense; its specific gravity
is 3.84, close to that of topaz
, and much denser than quartz
(specific gravity 2.5 to 2.7). It is easily soluble in hydrochloric acid
.
varies with the direction of propagation of the light, and varies between 1.64 and 1.75. This is quite high, between topaz
and ruby
. Lavendulan is biaxial (-)
, and most sources quote values for three refractive indices, for light travelling parallel to the three crystal axes. One source, however, gives lavendulan as nearly uniaxial (-)
, and quotes only two refractive indices, for the ordinary
and extraordinary rays
.
Lavendulan is pleochroic
, with O = pale blue to pale greenish blue and E = blue to greenish blue.
in the oxidised zone of some copper-arsenic deposits.
in the Erzgebirge, which is a mountainous region spanning the Czech Republic and Germany. The mineral was named “lavendulan” after the color, and Annaberg was the designated type locality. In 1853 Vogel found a specimen of lavendulan from Joachimstal
, also in the Erzgebirge, which was similar in appearance and characteristics to the material from Annaberg.
In 1877 Goldsmith examined some specimens of a turquoise blue arsenate of copper from the cobalt
deposits of San Juan, Chile, and announced that they were also lavendulan.
Nearly fifty years later, In 1924, William Foshag announced that the Chilean material was entirely distinct from that from Joachimstal, and he determined that it was a new mineral, and gave it the name freirinite, from the locality, the Blanca Mine, Freirina
, Huasca Province, Atacama Region, Chile.
In 1957, however, Claude Guillemin found that lavendulan and freirinite from the type localities gave identical x-ray powder patterns
, and freirinite was discredited as a mineral species.
Yet another fifty years passed, and in 2007 Geister et al re-examined Breithaupt’s type specimen and found that it was a mixture unrelated to modern lavendulan. The second locality where lavendulan was found is in the Czech Republic, so the type locality of the species was changed to there, namely St Joachimsthal, St Joachimsthal District, Erzgebirge, Karlovy Vary Region, Bohemia, Czech Republic.
The type material is held at the Mining Academy
, Freiberg, Germany, reference 20944.
, malachite
and cobaltian wad
. At the Cap Garonne Mine, Pradet
, Var, Provence-Alpes-Côte d'Azur, France, associated minerals are chalcophyllite
, cyanotrichite
, parnauite, mansfieldite, olivenite
, tennantite
, covellite
, chalcanthite
, antlerite
, brochantite
and geminite.
It also occurs at Tsumeb
, Namibia, associated with cuprian adamite
, conichalcite
, o’danielite, tsumcorite
, fahleite, quartz
, calcite
and gypsum
.
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...
arsenate
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]....
mineral, known for its characteristic intense electric blue color. It belongs to the lavendulan group, which has four members:
- Lavendulan NaCaCu5(AsO4)4Cl.5H2O
- Lemanskiite NaCaCu5(AsO4)4Cl.5H2O
- SampleiteSampleiteSampleite has a general formula of NaCaCu54Cl•5. It was first described in 1942 for an occurrence in Chuquicamata, Chile and was named after Mat Sample, a mine superintendent for the Chile Exploration Company....
NaCaCu5(PO4)4Cl.5H2O - Zdenĕkite NaPbCu5(AsO4)4Cl.5H2O
Lemanskiite and lavendulan are dimorphs
Polymorphism (materials science)
Polymorphism in materials science is the ability of a solid material to exist in more than one form or crystal structure. Polymorphism can potentially be found in any crystalline material including polymers, minerals, and metals, and is related to allotropy, which refers to chemical elements...
; they have the same formula, but different structures. Lemanskiite is tetragonal
Tetragonal crystal system
In crystallography, the tetragonal crystal system is one of the 7 lattice point groups. Tetragonal crystal lattices result from stretching a cubic lattice along one of its lattice vectors, so that the cube becomes a rectangular prism with a square base and height .There are two tetragonal Bravais...
, but lavendulan is monoclinic
Monoclinic crystal system
In crystallography, the monoclinic crystal system is one of the 7 lattice point groups. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal length, as in the orthorhombic system. They form a rectangular prism with a...
. Lavendulan has the same structure as sampleite, and the two minerals form a series. It is the calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...
analogue of zdenĕkite, and the arsenate
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]....
analogue of sampleite.
Lavendulan was originally named for the lavender color
Lavender (color)
Lavender is a pale tint of violet. It applies particularly to the color of the flower of the same name. The web color called lavender is displayed at right—it matches the color of the very palest part of the lavender flower; however, the more saturated color shown below as floral lavender more...
of the "type"
Type locality (geology)
Type locality , also called type area or type locale, is the where a particular rock type, stratigraphic unit, fossil or mineral species is first identified....
specimen, which has since been determined to be a mixture with no relationship to modern lavendulan. The mineral which is now called lavendulan is not a lavender blue color, and has no relationship to the “type” material from Annaberg. It often contains potassium
Potassium
Potassium is the chemical element with the symbol K and atomic number 19. Elemental potassium is a soft silvery-white alkali metal that oxidizes rapidly in air and is very reactive with water, generating sufficient heat to ignite the hydrogen emitted in the reaction.Potassium and sodium are...
, cobalt
Cobalt
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....
and nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
as impurities.
Unit cell
Although lavendulan is monoclinic, the angle β is very close to 90°, making the mineral pseudo-orthorhombicOrthorhombic crystal system
In crystallography, the orthorhombic crystal system is one of the seven lattice point groups. Orthorhombic lattices result from stretching a cubic lattice along two of its orthogonal pairs by two different factors, resulting in a rectangular prism with a rectangular base and height , such that a,...
. Most references describe the lavendulan unit cell as an orthorhombic cell containing 8 formula units (Z=8) but Mindat.org describes a monoclinic unit cell with the length of the c axis halved, and only 4 formula units per unit cell (Z=4) and space group
Space group
In mathematics and geometry, a space group is a symmetry group, usually for three dimensions, that divides space into discrete repeatable domains.In three dimensions, there are 219 unique types, or counted as 230 if chiral copies are considered distinct...
P21/n. Unit cell parameters are reported as
- a=9.73 Å, b=41.0 Å, c=9.85 Å, Z=8
- a = 9.815 Å, b = 40.394 Å, c = 9.99 Å, Z = 8
- a = 9.73 Å, b = 41.0 Å, c = 9.85 Å, Z = 8
- a = 10.011 Å, b = 19.478 Å, c = 10.056 Å, β = 90.37° Z=4
Physical properties
Lavendulan is a blue or greenish blue translucent mineral, with a vitreous to waxy lusterLustre (mineralogy)
Lustre is a description of the way light interacts with the surface of a crystal, rock, or mineral. The word lustre traces its origins back to the Latin word lux, meaning "light", and generally implies radiance, gloss, or brilliance....
, satiny in aggregates, and a light blue streak
Streak (mineralogy)
The streak of a mineral is the color of the powder produced when it is dragged across an unweathered surface. Unlike the apparent color of a mineral, which for most minerals can vary considerably, the trail of finely ground powder generally has a more consistent characteristic color, and is thus...
. It occurs as thin botryoidal crusts of minute radiating fibers or as thin rectangular, pseudo-orthorhombic plates, with cleavage
Cleavage (crystal)
Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite crystallographic structural planes. These planes of relative weakness are a result of the regular locations of atoms and ions in the crystal, which create smooth repeating surfaces that are visible both in the...
in three directions, nearly perfect perpendicular to the b crystal axis, and distinct perpendicular to the a and c axes. Twinning
Crystal 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....
is common. The mineral is brittle, with an uneven fracture
Fracture (mineralogy)
In the field of mineralogy, fracture is a term used to describe the shape and texture of the surface formed when a mineral is fractured. Minerals often have a highly distinctive fracture, making it a principal feature used in their identification....
. It is quite soft, with hardness
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...
2.5, between gypsum
Gypsum
Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...
and calcite
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:...
, and relatively dense; its specific gravity
Specific gravity
Specific gravity is the ratio of the density of a substance to the density of a reference substance. Apparent specific gravity is the ratio of the weight of a volume of the substance to the weight of an equal volume of the reference substance. The reference substance is nearly always water for...
is 3.84, close to that of topaz
Topaz
Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al2SiO42. Topaz crystallizes in the orthorhombic system and its crystals are mostly prismatic terminated by pyramidal and other faces.-Color and varieties:...
, and much denser than 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,...
(specific gravity 2.5 to 2.7). It is easily soluble in hydrochloric acid
Hydrochloric acid
Hydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
.
Optical properties
The refractive indexRefractive index
In optics the refractive index or index of refraction of a substance or medium is a measure of the speed of light in that medium. It is expressed as a ratio of the speed of light in vacuum relative to that in the considered medium....
varies with the direction of propagation of the light, and varies between 1.64 and 1.75. This is quite high, between topaz
Topaz
Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al2SiO42. Topaz crystallizes in the orthorhombic system and its crystals are mostly prismatic terminated by pyramidal and other faces.-Color and varieties:...
and ruby
Ruby
A ruby is a pink to blood-red colored gemstone, a variety of the mineral corundum . The red color is caused mainly by the presence of the element chromium. Its name comes from ruber, Latin for red. Other varieties of gem-quality corundum are called sapphires...
. Lavendulan is biaxial (-)
Birefringence
Birefringence, or double refraction, is the decomposition of a ray of light into two rays when it passes through certain anisotropic materials, such as crystals of calcite or boron nitride. The effect was first described by the Danish scientist Rasmus Bartholin in 1669, who saw it in calcite...
, and most sources quote values for three refractive indices, for light travelling parallel to the three crystal axes. One source, however, gives lavendulan as nearly uniaxial (-)
Birefringence
Birefringence, or double refraction, is the decomposition of a ray of light into two rays when it passes through certain anisotropic materials, such as crystals of calcite or boron nitride. The effect was first described by the Danish scientist Rasmus Bartholin in 1669, who saw it in calcite...
, and quotes only two refractive indices, for the ordinary
Birefringence
Birefringence, or double refraction, is the decomposition of a ray of light into two rays when it passes through certain anisotropic materials, such as crystals of calcite or boron nitride. The effect was first described by the Danish scientist Rasmus Bartholin in 1669, who saw it in calcite...
and extraordinary rays
Birefringence
Birefringence, or double refraction, is the decomposition of a ray of light into two rays when it passes through certain anisotropic materials, such as crystals of calcite or boron nitride. The effect was first described by the Danish scientist Rasmus Bartholin in 1669, who saw it in calcite...
.
- Nx = 1.645 Ny = 1.715 Nz = 1.725
- Nx = 1.660 Ny = 1.715 Nz = 1.734
- Nx = 1.66 Ny = 1.715 Nz = 1.734
- Nω = 1.748 Nε = 1.645.
Lavendulan is pleochroic
Pleochroism
Pleochroism is an optical phenomenon in which a substance appears to be different colors when observed at different angles with polarized light.- Background :Anisotropic crystals will have optical properties that vary with the direction of light...
, with O = pale blue to pale greenish blue and E = blue to greenish blue.
Environment
Lavendulan is a rare secondary mineralSupergene (geology)
In ore deposit geology, supergene processes or enrichment occur relatively near the surface. Supergene processes include the predominance of meteoric water circulation with concomitant oxidation and chemical weathering. The descending meteoric waters oxidize the primary sulfide ore minerals and...
in the oxidised zone of some copper-arsenic deposits.
Type locality
A lavender blue mineral was discovered in 1837 by Johann F A Breithaupt in AnnabergAnnaberg-Buchholz
Annaberg-Buchholz is a town in the Free State of Saxony, Germany, in the Erzgebirge, capital of the district Erzgebirgskreis.The town is located in the Ore Mountains, at the side of the Pöhlberg . It has three Protestant churches, among them that of St...
in the Erzgebirge, which is a mountainous region spanning the Czech Republic and Germany. The mineral was named “lavendulan” after the color, and Annaberg was the designated type locality. In 1853 Vogel found a specimen of lavendulan from Joachimstal
Jáchymov
For other places called Joachimsthal, see Joachimsthal Jáchymov . compl: "Sant Joachim's Sthal" is a spa town in north-west Bohemia in the Czech Republic belonging to the Karlovy Vary Region. It is situated at an altitude of 733 m above sea level in the eponymous St...
, also in the Erzgebirge, which was similar in appearance and characteristics to the material from Annaberg.
In 1877 Goldsmith examined some specimens of a turquoise blue arsenate of copper from the cobalt
Cobalt
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....
deposits of San Juan, Chile, and announced that they were also lavendulan.
Nearly fifty years later, In 1924, William Foshag announced that the Chilean material was entirely distinct from that from Joachimstal, and he determined that it was a new mineral, and gave it the name freirinite, from the locality, the Blanca Mine, Freirina
Freirina
Freirina is a Chilean commune and town in Huasco Province, Atacama Region. The commune spans an area of .-Demographics:According to the 2002 census by the National Statistics Institute, Freirina had 5,666 inhabitants; of these, 3,469 lived in urban areas and 2,107 in rural areas. At that time,...
, Huasca Province, Atacama Region, Chile.
In 1957, however, Claude Guillemin found that lavendulan and freirinite from the type localities gave identical x-ray powder patterns
Powder diffraction
Powder diffraction is a scientific technique using X-ray, neutron, or electron diffraction on powder or microcrystalline samples for structural characterization of materials.-Explanation:...
, and freirinite was discredited as a mineral species.
Yet another fifty years passed, and in 2007 Geister et al re-examined Breithaupt’s type specimen and found that it was a mixture unrelated to modern lavendulan. The second locality where lavendulan was found is in the Czech Republic, so the type locality of the species was changed to there, namely St Joachimsthal, St Joachimsthal District, Erzgebirge, Karlovy Vary Region, Bohemia, Czech Republic.
The type material is held at the Mining Academy
Technische Universität Bergakademie Freiberg
The Technische Universität Bergakademie Freiberg is a small German University of Technology with about 5000 students in the city of Freiberg, Saxony...
, Freiberg, Germany, reference 20944.
Occurrences
At the type locality, lavendulan occurs associated with erythrite and a cobalt molybdate originally called pateraite, but now discredited. At San Juan, Chile, it is associated with erythrite, cupriteCuprite
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...
, 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...
and cobaltian wad
Wad
Wad is an old mining term for any black manganese oxide or hydroxide mineral rich rock in the oxidized zone of various ore deposits. Typically closely associated with various iron oxides. Specific mineral varieties include pyrolusite, lithiophorite, nsutite, takanelite and vernadite....
. At the Cap Garonne Mine, Pradet
Le Pradet
Le Pradet is a commune in the Var department in the Provence-Alpes-Côte d'Azur region in southeastern France.Olive oil, vegetables and wine grape are produced in the local farms....
, Var, Provence-Alpes-Côte d'Azur, France, associated minerals are chalcophyllite
Chalcophyllite
Chalcophyllite is a rare secondary copper arsenate mineral occurring in the oxidized zones of some arsenic-bearing copper deposits. It was first described from material collected in Germany...
, cyanotrichite
Cyanotrichite
Cyanotrichite is a copper aluminium sulfate mineral, Cu4Al2[12|SO4]·2H2O, also known as lettsomite, very similar to halotrichite, and a member of the same group. However, it is much rarer. It forms velvety aggregates of extremely fine fibres and radial aggregates...
, parnauite, mansfieldite, olivenite
Olivenite
Olivenite is a copper arsenate mineral, formula Cu2AsO4OH. It crystallizes in the monoclinic system , and is sometimes found in small brilliant crystals of simple prismatic habit terminated by domal faces...
, tennantite
Tennantite
Tennantite is a copper arsenic sulfosalt mineral. Its chemical formula is Cu12As4S13. It is grey-black, steel-gray, iron-gray or black in color. A closely related mineral, tetrahedrite has antimony substituting for arsenic and the two form a solid solution series. The two have very similar...
, covellite
Covellite
Covellite is a rare copper sulfide mineral with the formula CuS. This indigo blue mineral is ubiquitous in copper ores, it is found in limited abundance and is not an important ore of copper itself, although it is well known to mineral collectors.The mineral is associated with chalcocite in zones...
, chalcanthite
Chalcanthite
Chalcanthite, whose name derives from the Greek, chalkos and anthos, meaning copper flower, is a richly-colored blue/green water-soluble sulfate mineral CuSO4·5H2O. It is commonly found in the late-stage oxidation zones of copper deposits...
, antlerite
Antlerite
Antlerite is a greenish hydrous copper sulfate mineral, with the formula Cu34. It occurs in tabular, acicular, or fibrous crystals with a vitreous luster...
, brochantite
Brochantite
Brochantite is a sulfate mineral, one of a number of cupric sulfates. Its chemical formula is CuSO4·3Cu2. Formed in arid climates or in rapidly oxidizing copper sulfide deposits, it is named for its discoverer, the French geologist and mineralogist, A. J. M...
and geminite.
It also occurs at Tsumeb
Tsumeb
Tsumeb is a city of 15,000 inhabitants and the largest town in Oshikoto region in northern Namibia. Tsumeb is the home of the world-famous Tsumeb mine, and the "gateway to the north" of Namibia. It is the closest town to the Etosha National Park...
, Namibia, associated with cuprian adamite
Adamite
Adamite is a zinc arsenate hydroxide mineral, Zn2AsO4OH. It is a mineral that typically occurs in the oxidized or weathered zone above zinc ore occurrences. Pure adamite is colorless, but usually it possess yellow color due to Fe compounds admixture. Tints of green also occur and are connected with...
, conichalcite
Conichalcite
Conichalcite, CaCu, is a relatively common arsenate mineral related to duftite . It is green, often botryoidal, and occurs in the oxidation zone of some metal deposits. It occurs with limonite, malachite, beudantite, adamite, cuproadamite, olivenite and smithsonite.- Formation :Conichalcite forms...
, o’danielite, tsumcorite
Tsumcorite
Tsumcorite is a rare hydrated lead arsenate mineral that was discovered in 1971, and reported by Geier, Kautz and Muller. It was named after the TSUMeb CORporation mine at Tsumeb, in Namibia, in recognition of the Corporation’s support for mineralogical investigations of the orebody at its Mineral...
, fahleite, 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,...
, calcite
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:...
and gypsum
Gypsum
Gypsum is a very soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula CaSO4·2H2O. It is found in alabaster, a decorative stone used in Ancient Egypt. It is the second softest mineral on the Mohs Hardness Scale...
.
External links
- Jmol: http://rruff.geo.arizona.edu/AMS/viewJmol.php?id=07151
- Lavendulan photo gallery at Mindat.orgMindat.orgMindat.org is a non-commercial online mineralogical database, claiming to be the largest mineral database and mineralogical reference website on the internet....