Melkovite
Chemical formula: CaFe<sup>3+</sup><sub>2</sub>Mo<sup>6+</sup><sub>5</sub>O<sub>10</sub>(PO<sub>4</sub>)<sub>2</sub>(OH)<sub>12</sub>·8H<sub>2</sub>O
Melkovite is a very rare, secondary molybdate-phosphate mineral, forming earthy coatings and aggregates with a characteristic lemon-yellow color.
Description
## Characteristics Melkovite is a complex, hydrated calcium and iron phosphate and molybdate. It occurs as earthy, powdery, or dusty aggregates, as well as in compact, cryptocrystalline masses. It does not form macroscopic crystals. Its most characteristic feature is its intense, lemon-yellow to greenish-yellow color, which distinguishes it in its natural environment. ## Physical Properties This mineral is very soft, with a Mohs hardness of approximately 2. It has a dull or earthy luster and is translucent to opaque. Its calculated density is approximately 3.35 g/cm³. Due to its structure and softness, it is very brittle. ## Colors and Varieties Melkovite occurs in shades of yellow, most commonly lemon-yellow, but is also found in greenish-yellow variants. No named varieties of this mineral are distinguished. ## History and Name The mineral's name, approved in 1968, honors Vyacheslav Gavrilovich Melkov (1911-1991), a Russian mineralogist and expert in the mineralogy of uranium and molybdenum deposits, who was a pioneer in the study of secondary uranium minerals. ## Uses Melkovite has no industrial application. Its significance is purely scientific and as a collector's item, as a very rare and unusual mineral species.
Diagnostic features
## Identification Key diagnostic features of melkovite include its characteristic lemon-yellow color, earthy or powdery habit, very low hardness, and specific occurrence environment. It typically forms thin coatings and crusts on the host rock. ## Distinguishing from Similar Minerals Melkovite can be confused with other secondary yellow minerals, such as ferrimolybdite or jarosite. Ferrimolybdite often forms fibrous or silky aggregates, in contrast to earthy melkovite. Jarosite, although sometimes similar in color, often occurs as small, shiny trigonal crystals. Certain differentiation of these minerals in many cases requires advanced chemical (EDS) or X-ray (XRD) analyses. ## Crystal Forms This mineral is cryptocrystalline and does not form crystals visible to the naked eye. It occurs exclusively in the form of earthy, dusty, and compact masses.
Geological environment
## Genesis Melkovite is a secondary mineral that forms in the oxidation zones of molybdenum-uranium deposits. Its formation is associated with the weathering processes of primary ore minerals in dry, hot climate conditions. ## Mineral Associations It most commonly co-occurs with other secondary molybdenum and iron minerals, such as ferrimolybdite, jarosite, and also with gypsum. ## Localities The only significant and typical occurrence of melkovite in the world is the Shabyr-Sai deposit in the Karaganda Region of Kazakhstan.
Rarity
Very rare
Collector aspects
## Quality Criteria As a mineral occurring mainly in microscopic form, its collector's value depends on the richness and intensity of the color of the coating on the host rock. Specimens where melkovite forms a distinct, well-colored crust, preferably accompanied by other rare secondary minerals, are most valued. ## Popular Localities All collector's specimens come from the type locality – the Shabyr-Sai deposit in Kazakhstan. This is the only source of this mineral on the market.
Care and storage
## Cleaning Due to its extreme softness and earthy form, this mineral should not be cleaned mechanically or with water. Any dust can only be removed with a very gentle stream of compressed air. ## What to Avoid Contact with water, chemicals, acids, and ultrasonic cleaners should be strictly avoided. The mineral is very brittle and sensitive to all forms of abrasion. It should be protected from moisture and temperature changes. ## Storage Melkovite specimens are best stored in tightly sealed micromount containers, which protect them from dust, moisture, and mechanical damage. They should be displayed away from sources of vibration.