Altaite
Chemical formula: Pb<sup>2+</sup>Te<sup>2-</sup>
Lead telluride with a metallic luster and perfect cubic cleavage, often found in association with gold.
Description
## Characteristics Altaite is a mineral from the telluride group, being naturally occurring lead telluride (PbTe). It forms isometric crystals, most commonly cubes and octahedra, although well-formed specimens are rare. It usually occurs as granular aggregates, massive impregnations, or as fine grains disseminated in rock. Its characteristic feature is a tin-white or yellowish-white color, which quickly tarnishes in air and becomes covered with a brownish-yellow or iridescent film. It has a strong, metallic luster. ## Physical properties This mineral is relatively soft, with a Mohs hardness of 2.5 to 3. It is also extremely dense – its specific gravity ranges from 8.1 to 8.2 g/cm³, which makes even small specimens surprisingly heavy. It is completely opaque. It is characterized by perfect cleavage in three mutually perpendicular directions, corresponding to the faces of a cube. ## Colors and varieties Altaite does not form color varieties. Its fresh surface is tin-white, often with a yellowish tint. When exposed to air, it quickly oxidizes, causing brownish-yellow, and sometimes variegated, iridescent films to form on the surface. ## History and name The mineral's name, given in 1845 by Wilhelm von Haidinger, comes from its first discovery location – the Altai Mountains in Kazakhstan. It was identified in material from the Zavodinsk mine (Заводинский рудник). ## Uses Altaite has no direct industrial application. However, it is an important mineral for collectors and scientists. Its presence can indicate the occurrence of gold and silver deposits, as it often accompanies valuable tellurides of these metals. It can be a minor source of tellurium.
Diagnostic features
## Identification The most important diagnostic features of altaite are its very high density (the specimen is extremely heavy for its size), tin-white color on a fresh fracture, blackish-gray streak, and perfect, three-directional cleavage, causing the mineral to break into small cubes. Its co-occurrence with other tellurides and gold is also characteristic. ## Distinguishing from similar minerals Altaite is sometimes confused with galena (PbS), which also has cubic cleavage and a metallic luster. However, altaite is much denser, has a lighter, more tin-like color, and a darker, blackish-gray streak (galena's streak is lead-gray). Unlike galena, altaite often occurs in association with gold and silver tellurides. ## Crystal forms Altaite crystals are rare and usually small. They take the form of cubes, less commonly octahedra or combinations thereof. It is most often found as granular aggregates, masses filling rock fractures, or as small inclusions in other minerals.
Geological environment
## Genesis Altaite is a typical hydrothermal mineral, forming in ore veins under low to medium temperature conditions. It forms in environments rich in tellurium and poor in sulfur. ## Mineral associations This mineral often co-occurs with other tellurides, such as sylvanite, calaverite, krennerite, petzite, and hessite. It is also commonly accompanied by native gold, pyrite, galena, chalcopyrite, sphalerite, tetrahedrite, and quartz, calcite, and dolomite as gangue minerals. ## Localities Important global localities include: Zavodinsk mine in the Altai Mountains (Kazakhstan) – the type locality; gold deposits in Kalgoorlie (Western Australia); Cripple Creek in Colorado and Calaveras County in California (USA); Săcărâmb (formerly Nagyág) in Romania; and the Kirkland Lake area in Ontario (Canada).
Rarity
Not very common
Collector aspects
## Quality criteria The most prized specimens by collectors are those where altaite occurs in association with well-formed native gold crystals or rare gold and silver tellurides. Rare, well-formed crystals of altaite itself are also highly valued, although they are usually microscopic in size. Rich, massive aggregates of this mineral are also valuable, especially those from classic, historical localities. ## Popular localities Specimens from Cripple Creek (Colorado, USA) and Kalgoorlie (Australia) are particularly sought after due to frequent and spectacular associations with gold. Săcărâmb in Romania is a classic European locality, from which historical specimens of scientific importance originate.
Care and storage
## Cleaning Altaite is a very soft, brittle, and oxidation-prone mineral. Only dry cleaning methods should be used, for example, a very soft brush to remove dust. Water and any chemical agents that may accelerate tarnishing or damage the surface should be avoided. ## What to avoid This mineral is sensitive to moisture and atmospheric oxygen, which cause it to tarnish and change color. It should be protected from impacts and scratching due to its low hardness and perfect cleavage. Ultrasonic cleaners and steam cleaning should be absolutely avoided. ## Storage It is recommended to store altaite specimens in sealed, airtight containers or "membrane boxes" to limit air access and slow down the oxidation process. It should be stored separately from harder minerals, in a padded box, to avoid mechanical damage.