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Sperrylite

earth science Maturity 7-9 Next article →

Sperrylite is a rare and significant platinum arsenide mineral. An arsenide is a chemical compound containing arsenic. This mineral is vital because it is the most common platinum mineral found in nature. It is characterized by its opaque, tin-white color and a brilliant metallic luster. Because it contains platinum, it is a key subject for geologists studying precious metals. It belongs to the pyrite group, which is a specific family of minerals with similar structures.

Sperrylite at Norilsk RU
Sperrylite at Norilsk RU

The internal structure of sperrylite is highly organized. It crystallizes in the isometric system, specifically within the space group Pa3. This organization allows it to form many different crystal habits. It can appear as cubes, octahedrons, or pyritohedrons. Some crystals show a reniform habit, which means they look somewhat kidney-shaped. In 1903, researchers Nicol and Goldschmidt identified seventeen different crystal forms. These include trapezohedra, trisoctahedrons, pyritohedra, and diploids. Some crystals even appear so modified that their edges and corners look rounded.

Sperrylite at Norilsk RU
Sperrylite at Norilsk RU

Sperrylite possesses several distinct physical properties. It has a Mohs hardness of 6 to 7. This means it is quite hard and resistant to scratching. It is also very dense. Its calculated specific gravity is 10.78, making it extremely heavy for its size. When it breaks, it shows a conchoidal fracture, which produces smooth, curved surfaces like broken glass. It is also brittle, meaning it will snap rather than bend under pressure. Additionally, the mineral is non-magnetic and non-radioactive. Its streak, which is the color left behind when rubbed on a surface, is grey to black.

The discovery of sperrylite is tied to the history of mining in Canada. In 1887, a chemist named Francis Louis Sperry collected ore from the Vermillion Mine. He was working for the Canadian Copper Company. He was performing a fire assay, a process used to determine gold content, when he encountered the material. In 1889, H. H. Wells officially described the mineral. Wells named it sperrylite to honor the work of Francis Sperry. This discovery took place within the Sudbury Basin, a major area for mineral research.

Sperrylite at Norilsk RU
Sperrylite at Norilsk RU

Geologists find sperrylite in several specific types of geological settings. It is most famously found in the nickel ore deposits of the Sudbury Basin in Ontario, Canada. It also occurs in the Bushveld layered igneous complex in South Africa. Another major location is the Oktyabr'skoye copper-nickel deposit near Noril'sk, Russia. It has also been identified in sulfide deposits in Finland. Because sperrylite does not decompose easily through normal weathering, it can be found in alluvial deposits. These are deposits found in riverbeds or streams. For example, tiny crystals were found in streams in Macon County, North Carolina.

Sperrylite at Norilsk RU
Sperrylite at Norilsk RU

Sperrylite rarely exists alone in the Earth's crust. It is often found closely associated with base metal sulfides. It is frequently found at the edges of or partially enclosed by minerals like pentlandite, pyrrhotite, or chalcopyrite. It can also be found with minerals such as cooperite, laurite, kotulskite, and merenskyite. Some occurrences show intergrowths with platinum-iron (Pt-Fe) alloys. Chemical analyses often reveal minor amounts of rhodium within the mineral. Trace amounts of copper, iron, and antimony are also sometimes reported.

Sperrylite at Norilsk RU
Sperrylite at Norilsk RU

Understanding sperrylite helps scientists map the complex history of the Earth's crust. The mineral forms through processes like contact metamorphism. This occurs when heat from magma changes the surrounding rocks. Evidence for this is seen in the triple point annealing contacts found with pyrrhotite grains. The presence of sperrylite in specific layers helps geologists understand how large igneous complexes formed. By studying its specific dimensions and chemical makeup, researchers gain insights into the movement of precious metals through the Earth's systems.

Sperrylite at Norilsk RU
Sperrylite at Norilsk RU
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