Marrite
Encyclopedia
Marrite is depicted by the chemical formula
PbAgAsS3. It is the arsenic
equivalent of mineral freieslebenite
(PbAgSbS3), but also displays close polyhedral
characteristics with sicherite and diaphorite. Marrite was named in honor of geologist John Edward Marr
(1857–1933) of Cambridge, England.
. The symmetry
reveals that this mineral
is composed of 3 axes
of unequal lengths. Two of the axes are perpendicular
at 90 degrees, while one axis intersects at an angle less than 90 degrees. Crystal
habit includes striated, meaning it forms parallel
lines along crystal faces; or tabular, meaning that structure dimensions are thin in 1 direction.
, 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
is essential for correctly identifying similar minerals. Marrite belongs to the biaxial optical class, which signifies that it has two optic axes. An optic axis is the direction of light that travels at 0 birefringence
, causing the mineral to appear isotropic. When viewing the indicatrix of biaxial minerals, both optic axes are always perpendicular
to one of the two circular sections.
of the Lengenbach quarry in Binntal, Valais
, Switzerland
. It is primarily formed because of hydrothermal activity, which involves water and high temperatures. Marrite is predominately found in dolomite
along with a variety of other sulfosalts.
Chemical formula
A chemical formula or molecular formula is a way of expressing information about the atoms that constitute a particular chemical compound....
PbAgAsS3. It is the arsenic
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...
equivalent of mineral freieslebenite
Freieslebenite
Freieslebenite is a rare sulfosalt mineral of antimony, lead and silver with formula AgPbSbS3 and molecular weight of 533.02 g/mol. It is an opaque non-fluorescent mineral which has a hydrothermal origin. It is metallic, with a specific gravity of 6.3 and a Mohs hardness of 2.5 - about that of a...
(PbAgSbS3), but also displays close polyhedral
Polyhedron
In elementary geometry a polyhedron is a geometric solid in three dimensions with flat faces and straight edges...
characteristics with sicherite and diaphorite. Marrite was named in honor of geologist John Edward Marr
John Edward Marr
John Edward Marr FGS FRS 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...
(1857–1933) of Cambridge, England.
Crystal habit
Marrite is part of the monoclinic crystal class, and 2⁄m point groupPoint group
In geometry, a point group is a group of geometric symmetries that keep at least one point fixed. Point groups can exist in a Euclidean space with any dimension, and every point group in dimension d is a subgroup of the orthogonal group O...
. The symmetry
Symmetry
Symmetry generally conveys two primary meanings. The first is an imprecise sense of harmonious or aesthetically pleasing proportionality and balance; such that it reflects beauty or perfection...
reveals that this mineral
Mineral
A mineral is a naturally occurring solid chemical substance formed through biogeochemical processes, having characteristic chemical composition, highly ordered atomic structure, and specific physical properties. By comparison, a rock is an aggregate of minerals and/or mineraloids and does not...
is composed of 3 axes
Cartesian coordinate system
A Cartesian coordinate system specifies each point uniquely in a plane by a pair of numerical coordinates, which are the signed distances from the point to two fixed perpendicular directed lines, measured in the same unit of length...
of unequal lengths. Two of the axes are perpendicular
Perpendicular
In geometry, two lines or planes are considered perpendicular to each other if they form congruent adjacent angles . The term may be used as a noun or adjective...
at 90 degrees, while one axis intersects at an angle less than 90 degrees. Crystal
Crystal
A crystal or crystalline solid is a solid material whose constituent atoms, molecules, or ions are arranged in an orderly repeating pattern extending in all three spatial dimensions. The scientific study of crystals and crystal formation is known as crystallography...
habit includes striated, meaning it forms parallel
Parallel (geometry)
Parallelism is a term in geometry and in everyday life that refers to a property in Euclidean space of two or more lines or planes, or a combination of these. The assumed existence and properties of parallel lines are the basis of Euclid's parallel postulate. Two lines in a plane that do not...
lines along crystal faces; or tabular, meaning that structure dimensions are thin in 1 direction.
Optical mineralogy
Under a microscope, marrite has a distinct anisotropic 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....
, 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
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...
is essential for correctly identifying similar minerals. Marrite belongs to the biaxial optical class, which signifies that it has two optic axes. An optic axis is the direction of light that travels at 0 birefringence
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...
, causing the mineral to appear isotropic. When viewing the indicatrix of biaxial minerals, both optic axes are always perpendicular
Perpendicular
In geometry, two lines or planes are considered perpendicular to each other if they form congruent adjacent angles . The term may be used as a noun or adjective...
to one of the two circular sections.
Occurrence
The only known occurrence of Marrite is the type localityType 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....
of the Lengenbach quarry in Binntal, Valais
Valais
The Valais is one of the 26 cantons of Switzerland in the southwestern part of the country, around the valley of the Rhône from its headwaters to Lake Geneva, separating the Pennine Alps from the Bernese Alps. The canton is one of the drier parts of Switzerland in its central Rhône valley...
, Switzerland
Switzerland
Switzerland name of one of the Swiss cantons. ; ; ; or ), in its full name the Swiss Confederation , is a federal republic consisting of 26 cantons, with Bern as the seat of the federal authorities. The country is situated in Western Europe,Or Central Europe depending on the definition....
. It is primarily formed because of hydrothermal activity, which involves water and high temperatures. Marrite is predominately found in 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....
along with a variety of other sulfosalts.