Nagyagite is a rare sulfide mineral

Sulfide mineral

The sulfide minerals are a class of minerals containing sulfide as the major anion. Some sulfide minerals are economically important as metal ores. The sulfide class also includes the selenides, the tellurides, the arsenides, the antimonides, the bismuthinides, the sulfarsenides and the sulfosalts...

 with known occurrence associated with gold ores. Nagyagite crystals are opaque

Opacity (optics)

Opacity is the measure of impenetrability to electromagnetic or other kinds of radiation, especially visible light. In radiative transfer, it describes the absorption and scattering of radiation in a medium, such as a plasma, dielectric, shielding material, glass, etc...

, monoclinic and dark grey to black coloured.

It was first described in 1845 for an occurrence at the type locality

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....

 of the Nagyag mine, Sacarîmb, Hunedoara

Hunedoara

Hunedoara is a city in Hunedoara County, Transylvania, Romania. It is located in southeastern Transylvania near the Poiana Ruscă Mountains, and administers five villages: Boş, Groş, Hăşdat, Peştişu Mare and Răcăştia....

, Romania

Romania

Romania is a country located at the crossroads of Central and Southeastern Europe, on the Lower Danube, within and outside the Carpathian arch, bordering on the Black Sea...

.

It occurs in gold–tellurium epithermal hydrothermal veins

Vein (geology)

In geology, a vein is a distinct sheetlike body of crystallized minerals within a rock. Veins form when mineral constituents carried by an aqueous solution within the rock mass are deposited through precipitation...

. Minerals associated with nagyagite include: altaite

Altaite

Altaite, or lead telluride, is a yellowish white mineral with an isometric crystal structure. Altaite is in the galena group of minerals as it shares many of properties of galena. Altaite has an unusually high density for a light-colored mineral...

, petzite

Petzite

The mineral petzite, Ag3AuTe2, is a soft, steel-gray telluride mineral generally deposited by hydrothermal activity. It forms isometric crystals, and is usually associated with rare tellurium and gold minerals, often with silver, mercury, and copper....

, stutzite

Stützite

Stützite or stuetzite is a silver telluride mineral with formula: Ag5−xTe3 or Ag7Te4.It was first described in 1951 from a museum specimen from Sacarimb, Romania. It was named for Austrian mineralogist Xavier Stütz ....

, sylvanite

Sylvanite

Sylvanite or silver gold telluride, Te2, is the most common telluride of gold.-Properties:The gold:silver ratio varies from 3:1 to 1:1. It is a metallic mineral with a color that ranges from a steely gray to almost white. It is closely related to calaverite, which is more purely gold telluride with...

, tellurantimony, coloradoite

Coloradoite

Coloradoite, also known as mercury telluride , is a rare telluride ore associated with metallic deposit . Gold usually occurs within tellurides as a high finess native-metal ....

, krennerite

Krennerite

Krennerite is an orthorhombic gold telluride mineral which can contain a relatively small amount of silver in the structure. The formula is AuTe2 varying to Te2. Both of the chemically similar gold-silver tellurides, calaverite and sylvanite are in the monoclinic crystal system, whereas krennerite...

,
native 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...

, native gold, proustite

Proustite

Proustite is a sulfosalt mineral consisting of silver sulfarsenide, Ag3AsS3, known also as light red silver or ruby silver ore, and an important source of the metal. It is closely allied to the corresponding sulfantimonide, pyrargyrite, from which it was distinguished by the chemical analyses of...

, rhodochrosite

Rhodochrosite

Rhodochrosite is a manganese carbonate mineral with chemical composition MnCO3. In its pure form, it is typically a rose-red color, but impure specimens can be shades of pink to pale brown. The streak is white. Its Mohs hardness varies between 3.5 and 4. Its specific gravity is 3.5 to 3.7. It...

, arsenopyrite

Arsenopyrite

Arsenopyrite is an iron arsenic sulfide . It is a hard metallic, opaque, steel grey to silver white mineral with a relatively high specific gravity of 6.1. When dissolved in nitric acid, it releases elemental sulfur. When arsenopyrite is heated, it becomes magnetic and gives off toxic fumes...

, sphalerite

Sphalerite

Sphalerite is a mineral that is the chief ore of zinc. It consists largely of zinc sulfide in crystalline form but almost always contains variable iron. When iron content is high it is an opaque black variety, marmatite. It is usually found in association with galena, pyrite, and other sulfides...

, tetrahedrite

Tetrahedrite

Tetrahedrite is a copper antimony sulfosalt mineral with formula: 12Sb4S13. It is the antimony endmember of the continuous solid solution series with arsenic bearing tennantite. Pure endmembers of the series are seldom if ever seen in nature. Of the two, the antimony rich phase is more common...

, calaverite

Calaverite

Calaverite, or gold telluride, is an uncommon telluride of gold, a metallic mineral with the chemical formula AuTe2, with approximately 3% of the gold replaced by silver. It was first discovered in Calaveras County, California in 1861, and was named for the county in 1868.The mineral often has a...

, tellurobismuthite

Tellurobismuthite

Tellurobismuthite is a telluride mineral: bismuth telluride . It has a trigonal structure and lattice parameters a=0.439 nm and c=3.06 nm. There are natural cleavage planes in the direction as the crystal is effectively lamellar in that plane. The Mohs hardness is 2 and the specific gravity is...

, galena

Galena

Galena is the natural mineral form of lead sulfide. It is the most important lead ore mineral.Galena is one of the most abundant and widely distributed sulfide minerals. It crystallizes in the cubic crystal system often showing octahedral forms...

 and pyrite

Pyrite

The mineral pyrite, or iron pyrite, is an iron sulfide with the formula FeS2. This mineral's metallic luster and pale-to-normal, brass-yellow hue have earned it the nickname fool's gold because of its resemblance to gold...

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