Rickardite

Chemical formula: Cu₂.₆₄-₃.₀₀Te₂

A rare copper telluride with a characteristic purplish-red color that quickly tarnishes in air.

## Characteristics Rickardite is a rare mineral from the sulfide group, specifically a copper telluride. Its most distinctive feature is an intense, purplish-red color on a fresh surface, which, however, very quickly loses its luster when exposed to air. The oxidizing surface becomes covered with a dull, dark, often bluish or black tarnish, which is a typical phenomenon for this mineral. It occurs mainly in massive, fine-grained aggregates, rarely forming visible crystals. ## Physical Properties Rickardite is a relatively soft mineral, with a Mohs hardness of 3.5. It has a high metallic luster on a fresh fracture, which quickly becomes dull. It is opaque and quite dense, with a density in the range of 7.54 g/cm³. It is also brittle. ## Colors and Varieties Freshly exposed rickardite has a striking, purplish-red color, resembling fresh copper. Upon oxidation, this color changes to dark purple, bluish, and finally black. There are no distinct color varieties or commercial names for it. ## History and Name The mineral was first described in 1903 by Waldemar T. Schaller. The name "rickardite" was given in honor of Thomas Arthur Rickard (1864-1953), a prominent mining engineer and geologist, who was an editor of industry journals and an authority on ore deposits. The type locality, from which the first described samples originated, is the Good Hope Mine in Gunnison County, Colorado, USA. ## Uses Due to its rarity, rickardite has no industrial significance. It is solely an object of interest for collectors of rare minerals and scientists studying telluride deposits.

Properties

Mohs hardness: 3.5
Color: Red-violet (fresh), darkens
Luster: Metallic
Streak: Red
Density: 7.54
Cleavage: None
Fracture: Irregular/Uneven
Transparency: Opaque
Crystal system: Orthorhombic

Diagnostic features

## Identification The key diagnostic feature of rickardite is its unique purplish-red color on a fresh surface and its rapid tarnishing and darkening upon exposure to air. High density and metallic luster (on a fresh fracture) are also helpful. It is a soft and brittle mineral. ## Distinguishing from Similar Minerals Rickardite can be confused with bornite, which also exhibits purplish iridescence; however, bornite usually has more variegated, blue-violet tarnish colors on a brownish-copper background, whereas fresh rickardite is uniformly purplish-red. Weissite (another copper telluride) is darker, usually bluish-black. Dyscrasite is silvery-white. A fresh surface of rickardite is difficult to confuse with any other mineral. ## Crystal Forms Rickardite very rarely forms well-developed crystals. It usually occurs as massive, granular, or compact aggregates embedded in the host rock or other minerals. If crystals are present, they are in the form of small, hexagonal plates.

Geological environment

## Genesis Rickardite is a hydrothermal mineral. It forms in the final, low-temperature stages of crystallization in ore veins, in an environment rich in tellurium and poor in sulfur. It is a product of processes occurring at relatively low temperatures. ## Mineral Associations This mineral often co-occurs with other tellurides and ore minerals. Its typical associations include: native tellurium, weissite, petzite, sylvanite, vulcanite, pyrite, bornite, and quartz. ## Localities The most important and classic localities for rickardite are in the USA, particularly the Good Hope Mine (type locality) in Colorado and the Campbell Mine in Bisbee, Arizona. It is also known from the Kidston Mine in Queensland (Australia), the Kalgoorlie region in Western Australia, the Balan Mine in Romania, and several localities in Kazakhstan and the Urals in Russia.

Rarity

Very rare

For collectors

## Quality Criteria The most valued specimens by collectors are rickardite samples with the largest possible fresh surface exhibiting an intense, purplish-red color. Rich, massive aggregates in quartz or another contrasting mineral are highly prized. Due to the extreme rarity of well-formed crystals, any specimen with visible, even small, crystals is considered exceptional. The purity of the specimen and a minimal amount of mechanical damage also increase its value. ## Popular Localities The best specimens in the world are considered to be those from historical finds at the Campbell Mine in Bisbee, Arizona, USA. These are recognized as classics for this mineral and fetch the highest prices on the collector's market.

Care and storage

## Cleaning Rickardite is a very delicate mineral and sensitive to oxidation. Cleaning should be kept to an absolute minimum. If necessary, a soft brush can be used to remove dust. Avoid any contact with water and chemical agents. ## What to Avoid Absolutely avoid water, acids, detergents, and other chemicals. The mineral reacts very easily with oxygen from the air, causing tarnishing and color change – this is a natural process that cannot be completely stopped but can be slowed down by proper storage. It should not be heated or exposed to moisture. ## Storage Rickardite specimens are best stored in airtight, dust-free containers or "perky boxes" to limit contact with air and moisture. The use of desiccants can be considered. Storing in stable room conditions, away from heat and light sources, will help preserve its appearance for longer.