Leightonite is a rare sulfate mineral

Sulfate mineral

The sulfate minerals are a class of minerals which include the sulfate ion within their structure. The sulfate minerals occur commonly in primary evaporite depositional environments, as gangue minerals in hydrothermal veins and as secondary minerals in the oxidizing zone of sulfide mineral deposits...

 with formula of K₂Ca₂Cu(SO₄)₄•2H₂O.

Crystal class

Leightonite forms flattened to elongated bladed crystals of variously interpreted crystal structure. It’s crystal system is reported as triclinic morphologically, but also as pseudo-orthorhombic due to intricate lamellar twinning that mimics orthorhombic symmetry. Because it is triclinic, the crystal is represented by a system of three unequal vectors with corresponding unequal angles between them.

Optical class

Leightonite is anisotropic

Anisotropy

Anisotropy is the property of being directionally dependent, as opposed to isotropy, which implies identical properties in all directions. It can be defined as a difference, when measured along different axes, in a material's physical or mechanical properties An example of anisotropy is the light...

, meaning it has more than one refractive index

Refractive 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....

, in this case three as it is biaxial. The mineral can split polarized light into two rays with different direction and velocity, resulting in the appearance of interference colors when recombined and viewed under polarized light.

Discovery and occurrence

It was first described in 1938 for an occurrence in the Chuquicamata Mine

Chuquicamata

Chuquicamata, or "Chuqui" as it is more familiarly known, is by digged volume the biggest open pit copper mine in the world, located in the north of Chile, 215 km northeast of Antofagasta and 1,240 km north of the capital, Santiago...

, Calama

Calama

Calama may refer to:*Algeria**Guelma, an Algerian city once named Calama by ancient Roman settlers*Brazil**Calama, Rondônia*Chile**Calama, Chile*United States**Kalama, Washington or Kalama/Calama River*Calama...

, El Loa Province

El Loa Province

El Loa Province is one of three provinces of the northern Chilean region of Antofagasta . It is named after the longest of rivers in Chile, the Loa River...

, Antofagasta Region

Antofagasta Region

The II Antofagasta Region is one of Chile's fifteen first-order administrative divisions. It comprises three provinces, Antofagasta, El Loa and Tocopilla...

, 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...

, and named in honor of Tomas Leighton Donoso (1896–1967), Professor of Mineralogy at the University of Santiago, Chile.

It occurs in alkali oxidized zones of copper deposits and is associated with natrochalcite, blodite

Blödite

Blödite is a hydrated sodium magnesium sulfate mineral with formula: Na2Mg2·4H2O.The mineral is clear to yellow in color and forms monoclinic crystals. A synonym for the mineral is bloedite ....

, atacamite

Atacamite

Atacamite is a copper halide mineral: a copper chloride hydroxide with formula Cu2Cl3.It was first described for deposits in the Atacama Desert of Chile in 1801....

, bellingerite, kröhnkite

Kröhnkite

Kröhnkite is a rare copper sulfate mineral named after B. Kröhnke who first researched it.-Crystallography:Kröhnkite has monoclinic symmetry . Monoclinic symmetry implies that the mineral contains three axes of differing length , two of which intersect each other at 90° and one that intersects at...

, 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 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,...

 in the discovery location

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....

 at Chuquicamata, Chile; and with 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...

, anhydrite

Anhydrite

Anhydrite is a mineral – anhydrous calcium sulfate, CaSO4. It is in the orthorhombic crystal system, with three directions of perfect cleavage parallel to the three planes of symmetry. It is not isomorphous with the orthorhombic barium and strontium sulfates, as might be expected from the...

 and lammerite 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

Namibia

Namibia, officially the Republic of Namibia , is a country in southern Africa whose western border is the Atlantic Ocean. It shares land borders with Angola and Zambia to the north, Botswana to the east and South Africa to the south and east. It gained independence from South Africa on 21 March...

. It has also been reported from the Schwaz area of North Tyrol

North Tyrol

North Tyrol, or North Tirol is the main part of the Austrian state of Tyrol, located in the western part of the country. The other part of the state is East Tyrol, which also belongs to Austria, but does not share a border with North Tyrol....

, Austria

Austria

Austria , officially the Republic of Austria , is a landlocked country of roughly 8.4 million people in Central Europe. It is bordered by the Czech Republic and Germany to the north, Slovakia and Hungary to the east, Slovenia and Italy to the south, and Switzerland and Liechtenstein to the...

, and the Visdalen Soapstone Quarry, Lom

Lom, Norway

Lom is a municipality in Oppland county, Norway. It is part of the traditional region of Gudbrandsdal. The administrative centre of the municipality is the village of Fossbergom....

, Norway

Norway

Norway , officially the Kingdom of Norway, is a Nordic unitary constitutional monarchy whose territory comprises the western portion of the Scandinavian Peninsula, Jan Mayen, and the Arctic archipelago of Svalbard and Bouvet Island. Norway has a total area of and a population of about 4.9 million...

.

At the mining site of Chuquicamata, Chile, Leightonite is not found in rich ore; rather it only appears in borderland material within 50 meters of the surface, acting as a cement between rock fragments as it fills in cracks and cross-fiber veins in surfaces as a network of crystals. Although a hydrous sulfate of copper, it is not a major source of the element. Because of its rare nature, it is valued by mineral collectors.