Marrite (mar'-ite) is a

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. ...

with the

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...

PbAgAsS₃. It is the

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, bu ...

equivalent of freieslebenite (PbAgSbS₃), but also displays close polyhedral characteristics with sicherite and diaphorite.Berlepsch, P., Makovicky E., and Armbruster, T. (2002) Structural relationships between sicherite, marrite, freieslebenite, and diaphorite: Analysis based on anionic nets and polyhedral characteristics(178th edition) 75-91 p. E. Schweizerbart'sche Verlagsbuchhandlung. Stuttgart, Germany. Marrite was named in honor of geologist

John Edward Marr John Edward Marr FGS FRS (14 June 1857 – 1 October 1933) was a British geologist. After studying at Lancaster Royal Grammar School, he matriculated to St John's College, Cambridge, graduating with First Class Honours in 1878. Following under ...

(1857–1933) of

Cambridge, England Cambridge ( ) is a university city and the county town in Cambridgeshire, England. It is located on the River Cam approximately north of London. As of the 2021 United Kingdom census, the population of Cambridge was 145,700. Cambridge beca ...

."Marrite Mineral Data." http://webmineral.com/data/Marrite.shtml. Retrieved 8 September 2010.

Crystal habit

Marrite is part of the

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 ...

crystal class In crystallography, a crystallographic point group is a set of symmetry operations, corresponding to one of the point groups in three dimensions, such that each operation (perhaps followed by a translation) would leave the structure of a crystal un ...

, and ²⁄_m

point group In geometry, a point group is a mathematical group of symmetry operations ( isometries in a Euclidean space) that have a fixed point in common. The coordinate origin of the Euclidean space is conventionally taken to be a fixed point, and every ...

.Anthony, J.W., Bideaux, R.A., Bladh, K.W., and Nichols, M.C. (1990) Marrite. Handbook of Mineralogy. 313 p. Mineral Data Publication. Tucson, Arizona.
/ref> The symmetry reveals that this

is composed of 3

axes Axes, plural of '' axe'' and of '' axis'', may refer to * ''Axes'' (album), a 2005 rock album by the British band Electrelane * a possibly still empty plot (graphics) A plot is a graphical technique for representing a data set, usually as a g ...

of unequal lengths. Two of the axes are

perpendicular In elementary geometry, two geometric objects are perpendicular if they intersect at a right angle (90 degrees or π/2 radians). The condition of perpendicularity may be represented graphically using the ''perpendicular symbol'', ⟂. It can ...

at 90 degrees, while one axis intersects at an angle less than 90 degrees.

Crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macr ...

habit includes striated, meaning it forms

parallel Parallel is a geometric term of location which may refer to: Computing * Parallel algorithm * Parallel computing * Parallel metaheuristic * Parallel (software), a UNIX utility for running programs in parallel * Parallel Sysplex, a cluster of I ...

lines along crystal faces; or tabular, meaning that structure dimensions are thin in 1

direction Direction may refer to: *Relative direction, for instance left, right, forward, backwards, up, and down ** Anatomical terms of location for those used in anatomy ** List of ship directions *Cardinal direction Mathematics and science *Direction ...

Optical mineralogy

Under a microscope, marrite has a distinct

anisotropic Anisotropy () is the property of a material which allows it to change or assume different properties in different directions, as opposed to isotropy. It can be defined as a difference, when measured along different axes, in a material's phys ...

refractive index 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, o ...

, meaning the velocity of light varies depending on the direction being traveled through the mineral. It is typical of anisotropic minerals to display colorful, optical properties when viewed under cross polarized light. This differs from its vague gray color when viewed in plane polarized light, which is the reason

optical mineralogy Optical mineralogy is the study of minerals and rocks by measuring their optical properties. Most commonly, rock and mineral samples are prepared as thin sections or grain mounts for study in the laboratory with a petrographic microscope. Opti ...

is essential for correctly identifying similar minerals."Marrite Mineral Information and Data." http://www.mindat.org/min-2579.html. Retrieved 8 September 2010. Marrite belongs to the biaxial optical class, which signifies that it has two optic axes. An

optic axis An optical axis is a line along which there is some degree of rotational symmetry in an optical system such as a camera lens, microscope or telescopic sight. The optical axis is an imaginary line that defines the path along which light propagat ...

is the direction of light that travels at 0

birefringence Birefringence is the optical property of a material having a refractive index that depends on the polarization and propagation direction of light. These optically anisotropic materials are said to be birefringent (or birefractive). The birefrin ...

, causing the mineral to appear isotropic. When viewing the indicatrix of biaxial minerals, both optic axes are always

to one of the two circular sections.

Occurrence

The only known occurrence of Marrite is the

type locality Type locality may refer to: * Type locality (biology) * Type locality (geology) See also * Local (disambiguation) * Locality (disambiguation) {{disambiguation ...

of the Lengenbach quarry in

Binntal The Binn Valley ( German: ''Binntal'') is a valley of the Alps, located on the north side of the Lepontine Alps in the Swiss canton of Valais. The valley is drained by the ''Binna'', a tributary of the Rhone, at Grengiols. The valley is named ...

Valais Valais ( , , ; frp, Valês; german: Wallis ), more formally the Canton of Valais,; german: Kanton Wallis; in other official Swiss languages outside Valais: it, (Canton) Vallese ; rm, (Chantun) Vallais. is one of the 26 cantons forming the S ...

, Switzerland. It is primarily formed because of

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 ...

activity, which involves water and high

temperatures Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measured with a thermometer. Thermometers are calibrated in various temperature scales that historically have relied on ...

. Marrite is predominantly found in dolomite along with a variety of other

sulfosalt Sulfosalt minerals are sulfide minerals with the general formula , where *A represents a metal such as copper, lead, silver, iron, and rarely mercury, zinc, vanadium *B usually represents semi-metal such as arsenic, antimony, bismuth, and rarel ...

References

{{Reflist Arsenic minerals Lead minerals Silver minerals Sulfosalt minerals Monoclinic minerals Minerals in space group 14