Köttigite is a rare hydrated

zinc Zinc is a chemical element with the symbol Zn and atomic number 30. Zinc is a slightly brittle metal at room temperature and has a shiny-greyish appearance when oxidation is removed. It is the first element in group 12 (IIB) of the periodi ...

arsenate The arsenate ion is . An arsenate (compound) 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). Arsenate res ...

which was discovered in 1849 and named by

James Dwight Dana James Dwight Dana FRS FRSE (February 12, 1813 – April 14, 1895) was an American geologist, mineralogist, volcanologist, and zoologist. He made pioneering studies of mountain-building, volcanic activity, and the origin and structure of continent ...

in 1850 in honour of Otto Friedrich Köttig (18241892), a German chemist from

Schneeberg, Saxony Schneeberg is a town in Saxony’s district of Erzgebirgskreis. It has roughly 16,400 inhabitants and belongs to the Town League of Silberberg (''Städtebund Silberberg''). It lies 4 km west of Aue, and southeast of Zwickau. Geography ...

, who made the first chemical analysis of the mineral. It has the formula and it is a dimorph of metaköttigite, which means that the two minerals have the same formula, but a different structure: köttigite is

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic s ...

and metaköttigite is

triclinic 180px, Triclinic (a ≠ b ≠ c and α ≠ β ≠ γ ) In crystallography, the triclinic (or anorthic) crystal system is one of the 7 crystal systems. A crystal system is described by three basis vectors. In the triclinic system, the crystal i ...

. There are several minerals with similar formulae but with other

cations An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by con ...

in place of the zinc.

Iron Iron () is a chemical element with Symbol (chemistry), symbol Fe (from la, Wikt:ferrum, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 element, group 8 of the periodic table. It is, Abundanc ...

forms parasymplesite ;

cobalt Cobalt is a chemical element with the symbol Co and atomic number 27. As with nickel, cobalt is found in the Earth's crust only in a chemically combined form, save for small deposits found in alloys of natural meteoric iron. The free element, p ...

forms the distinctively coloured pinkish purple mineral erythrite and

nickel Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow ...

forms annabergite . Köttigite forms

series Series may refer to: People with the name * Caroline Series (born 1951), English mathematician, daughter of George Series * George Series (1920–1995), English physicist Arts, entertainment, and media Music * Series, the ordered sets used in ...

with all three of these minerals and they are all members of the vivianite group. The Vivianite Group is a group of

phosphates In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...

and

s with

divalent In chemistry, the valence (US spelling) or valency (British spelling) of an chemical element, element is the measure of its combining capacity with other atoms when it forms chemical compounds or molecules. Description The combining capacity, ...

. The group members are

annabergite Annabergite is an arsenate mineral consisting of a hydrous nickel arsenate, Ni3(AsO4)2·8H2O, crystallizing in the monoclinic system and isomorphous with vivianite and erythrite. Crystals are minute and capillary and rarely met with, the mineral ...

, arupite, babanekite, baricite,

erythrite Erythrite or red cobalt is a secondary hydrated cobalt arsenate mineral with the formula . Erythrite and annabergite, chemical formula , or nickel arsenate form a complete series with the general formula . Erythrite crystallizes in the monocli ...

, hornesite, kottingite, manganhornesite, pakhomovskyite, parasymplesite and vivianite.

Structure

Köttigite belongs to the

monoclinic crystal system In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in the orthorhombic ...

, so it has two crystal axes, a and c, inclined to each other at angle β, and a third axis, the b axis, at right angles to both a and c. It belongs to point group 2/m, which means that it has a two-fold axis of

rotational symmetry Rotational symmetry, also known as radial symmetry in geometry, is the property a shape has when it looks the same after some rotation by a partial turn. An object's degree of rotational symmetry is the number of distinct orientations in which i ...

parallel to b, and a mirror plane perpendicular to it. The space group is C2/m, which means that the

unit cell In geometry, biology, mineralogy and solid state physics, a unit cell is a repeating unit formed by the vectors spanning the points of a lattice. Despite its suggestive name, the unit cell (unlike a unit vector, for example) does not necessaril ...

is centred on the C face. Although zinc is the only transition metal that appears in the formula, köttigite usually contains significant quantities of

and

, and these three elements are randomly distributed over the cation sites to form complex slabs perpendicular to the b axis. These sheets are held together by

hydrogen bonding In chemistry, a hydrogen bond (or H-bond) is a primarily electrostatic force of attraction between a hydrogen (H) atom which is covalently bound to a more electronegative "donor" atom or group (Dn), and another electronegative atom bearing a l ...

alone, which is quite weak, hence the perfect cleavage in this direction.
There are two formula units per

(Z = 2) and the cell parameters are a = 10.24 Å, b = 13.405 Å, c = 4.757 Å and β = 105.21°.

Appearance

Pure end-member köttigite is colourless, but frequently samples are coloured pink, red, red-orange or brown by elements substituting for the zinc. It is light rose-pink in transmitted light, translucent with a reddish-white to white streak and a resinous or waxy lustre, silky on

fractures Fracture is the separation of an object or material into two or more pieces under the action of stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displa ...

. Crystals are small,

prismatic An optical prism is a transparent optical element with flat, polished surfaces that are designed to refract light. At least one surface must be angled — elements with two parallel surfaces are ''not'' prisms. The most familiar type of optical ...

parallel to the c axis and flattened perpendicular to the b axis. It also occurs as massive crusts with a crystalline surface and fibrous structure.

Optical properties

The mineral is biaxial (+) with

refractive indices In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium. The refractive index determines how much the path of light is bent, or ...

n_α = 1.622, n_β = 1.638 and n_γ = 1.671. The maximum birefringence δ is the difference between the largest and the smallest refractive index, and is equal to 0.049. Biaxial crystals have two optic axes, and the angle between them is known as the optic angle, 2V. For köttigite 2V has a measured value of 74°, and a calculated value of 72°.
Biaxial crystals have three mutually perpendicular principal optical direction, named X, Y and Z. Light travels at different speeds in different directions through the crystal. X is the direction of travel at the highest speed, Z at the lowest, and Y intermediate. The orientation is given by expressing the relationship of X, Y and Z to the crystallographic axes a, b and c. In monoclinic crystals one of the principal optical directions X, Y and Z coincides with the b axis. Since X, Y and Z are mutually perpendicular, it suffices to define just two of them, then the third is determined. For köttigite X=b and Z^c=37°.

Pleochroism Pleochroism (from Greek πλέων, ''pléōn'', "more" and χρῶμα, ''khrôma'', "color") is an optical phenomenon in which a substance has different colors when observed at different angles, especially with polarized light. Backgrou ...

is visible, with the crystal appearing colourless when viewed along X or Y, and pale red when viewed along Z. Pleochroism should not be present if the mineral is colourless. It is not

fluorescent Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, ...

Physical properties

Köttigite is soft, with

Mohs hardness The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by t ...

only to 3, even softer than calcite, which has a hardness of 3. It is also fairly light, with

specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its densest ...

3.33. Because of its sheetlike structure it has perfect cleavage perpendicular to the b axis; it is flexible, and has a fibrous fracture giving it a silky lustre on cleavage surfaces. It is soluble in acids.

Occurrence and associations

It is formed by the alteration of

smaltite Smaltite is a variety of the mineral skutterudite consisting of cobalt, iron, nickel, and arsenide. It has the chemical formula . Smaltite crystallizes in the cubic system with the same hemihedral symmetry as pyrite; crystals have usually the ...

and sphalerite . in oxidized zones of

arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, ...

al ores containing

. The type locality is the Daniel Mine (St. Daniel Mine), Neustädtel, Schneeberg District, Erzgebirge, Saxony, Germany, where it occurs in oxidized

veins Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenated b ...

in a

hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...

sulfide

ore deposit Ore is natural rock or sediment that contains one or more valuable minerals, typically containing metals, that can be mined, treated and sold at a profit.Encyclopædia Britannica. "Ore". Encyclopædia Britannica Online. Retrieved 7 April ...

, associated with roselite . At the Ojuela Mine,

Mapimí Municipality Mapimí is one of the 39 municipalities of Durango, in north-western Mexico. The municipal seat lies at Mapimí. The municipality covers an area of 7,126.7 km². In 2010, the municipality had a total population of 25,137, up from 22,940 in 2 ...

Mexico Mexico (Spanish: México), officially the United Mexican States, is a country in the southern portion of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatema ...

, it occurs in sprays of bladed crystals to 6 mm, which is large for the species, associated with symplesite , parasymplesite , adamite , legrandite , metaköttigite and

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, blackboard or sidewalk chalk, and drywal ...

. At the Hilton Mine,

Cumbria Cumbria ( ) is a ceremonial and non-metropolitan county in North West England, bordering Scotland. The county and Cumbria County Council, its local government, came into existence in 1974 after the passage of the Local Government Act 1972. C ...

, England, köttigite has been found in a specimen of galena and

gersdorffite Gersdorffite is a nickel arsenic sulfide mineral with formula NiAsS. It crystallizes in the isometric system showing diploidal symmetry. It occurs as euhedral to massive opaque, metallic grey-black to silver white forms. Gersdorffite belongs to ...

(but no sphalerite), on a surface coated with

and an earthy crust. The individual crystals are colourless, transparent, and very small, the largest being about 1 mm. At Bou Azzer, Taznakht,

Morocco Morocco (),, ) officially the Kingdom of Morocco, is the westernmost country in the Maghreb region of North Africa. It overlooks the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria t ...

, köttigite has been identified in a sample of

vein Veins are blood vessels in humans and most other animals that carry blood towards the heart. Most veins carry deoxygenated blood from the tissues back to the heart; exceptions are the pulmonary and umbilical veins, both of which carry oxygenat ...

quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...

rich in

chalcopyrite Chalcopyrite ( ) is a copper iron sulfide mineral and the most abundant copper ore mineral. It has the chemical formula CuFeS2 and crystallizes in the tetragonal system. It has a brassy to golden yellow color and a hardness of 3.5 to 4 on the Mo ...

and sphalerite . The sample has turquoise-blue secondary minerals including

devilline Devilline is a sulfate mineral with the chemical formula CaCu4(SO4)2(OH)6•3H2O. The name originates from the French chemist's name, Henri Etienne Sainte-Claire Deville (1818–1881). Devilline crystallizes in the monoclinic system. Crystallogr ...

, and also lath-shaped, blue-grey to pinkish grey crystals of köttigite with a habit resembling

, measuring less than 2 mm. The crystals are relatively rich in iron and cobalt, with traces of

copper Copper is a chemical element with the symbol Cu (from la, cuprum) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkis ...

and

References

{{DEFAULTSORT:Kottigite Zinc minerals Arsenate minerals Monoclinic minerals Minerals in space group 12 Vivianite group Minerals described in 1850