Almagreraite
Chemical formula: Cu<sup>2+</sup>Zn<sup>2+</sup>Mn<sup>4+</sup><sub>3</sub>O<sub>8</sub>
Almagrerait is a very rare, hydrated zinc, iron, and copper arsenate, forming greenish, platy crystals.
Description
## Characteristics Almagrerait is a mineral from the arsenate group, occurring as aggregates of very thin, flexible, and slightly curved platy crystals, reaching up to 0.2 mm in length. It forms characteristic spherical (spherulitic) aggregates and crusts on other minerals, mainly on goethite. Its appearance is delicate, and individual plates tend to bend. ## Physical Properties Almagrerait crystals exhibit a pearly luster on cleavage surfaces and a vitreous luster on other faces. The mineral is translucent. Its Mohs hardness is about 2, making it very soft. The calculated density is 3.19 g/cm³. It has perfect cleavage in one direction. ## Colors and Varieties This mineral occurs in uniform shades, from yellowish-green to apple-green. The streak on a porcelain plate is light greenish-yellow. No color or commercial varieties have been distinguished. ## History and Name The name almagrerait comes from its discovery locality – the Sierra Almagrera mountain range in Andalusia (Spain). It was officially recognized as a new mineral species by the International Mineralogical Association (IMA) in 2018. Its type locality is the "Teresa" mine. ## Uses Due to its extreme rarity and occurrence as microscopic crystals, almagrerait has no industrial applications. It is solely an object of scientific and collecting interest for specialists who collect rare minerals.
Diagnostic features
## Identification The characteristic features of almagrerait are its apple-green color, pearly luster on the plates, specific form of occurrence as spherical aggregates, and mineral paragenesis. In field conditions and in a collection, its visual identification is very difficult. Reliable identification requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical microanalysis (EDS). ## Distinguishing from Similar Minerals Almagrerait can be confused with many other secondary green arsenate minerals, such as annabergite, köttigite, some varieties of olivenite, conichalcite, or scorodite. Distinguishing it based on visual characteristics is practically impossible. Key to identification are its unique chemical composition (simultaneous presence of zinc, iron, and copper) and characteristic diffraction pattern. ## Crystal Forms Almagrerait forms aggregates of very small, thin, and flexible plates, which are often slightly bent. These plates arrange themselves into radial or spherical aggregates (spherulites) and thin crusts.
Geological environment
## Genesis Almagrerait is a secondary mineral, formed in the oxidation (supergene) zone of polymetallic hydrothermal deposits. It crystallizes as a result of weathering and alteration of primary sulfides (e.g., sphalerite) and arsenides in an arsenic-rich environment. ## Mineral Associations This mineral occurs in association with other secondary minerals, such as goethite, hematite, arseniosiderite, pharmacosiderite, olivenite, cornwallite, and scorodite. ## Localities The only confirmed locality of almagrerait in the world is its type locality – the "Teresa" mine in the Sierra Almagrera range, in the province of Almería in Spanish Andalusia.
Rarity
Extremely rare
Collector aspects
## Quality Criteria In the case of such a rare micromineral as almagrerait, the main criterion for collecting value is the richness of the specimen – that is, the degree of rock matrix coverage by crystals. The quality of spherulitic aggregate formation and the presence of well-defined associated minerals are also important. Aesthetics are less important than the scientific and documentary value of the specimen. ## Popular Localities As this mineral is known from only one locality in the world, all collectible specimens come from the "Teresa" mine in Spain. They are extremely difficult to acquire and are found mainly in specialized collections and scientific institutions.
Care and storage
## Cleaning Almagrerait specimens are extremely delicate and soft, so they should be handled with great care. For dust removal, it is best to use canned compressed air, applied from a safe distance. Mechanical cleaning with brushes is not recommended. Contact with water should be minimized; if necessary, use distilled water and dry the specimen immediately. ## What to Avoid As an arsenate, this mineral is toxic. Avoid inhaling dust and always wash hands after any contact. Almagrerait is a hydrated mineral, sensitive to high temperatures, which can cause dehydration and structural damage. It should be protected from acids and other chemicals. Due to its low hardness, it is susceptible to scratching. ## Storage It is recommended to store specimens in closed, padded "micromount" boxes, which protect against mechanical damage, dust, and sudden changes in humidity. Each specimen should be properly labeled with a warning about its arsenic content.