Sarrochite

Chemical formula: [Ca₄(H₂O)₃₈][Mo⁶⁺₈P₂Fe³⁺₃O₃₇(OH)]

Sarrochite is an extremely rare, complex molybdate discovered in Italy, forming microscopic, hexagonal, yellow crystals.

## Characteristics Sarrochite is a very complex hydrated calcium, phosphorus, and iron molybdate. It occurs as extremely small, hexagonal, tabular crystals, which rarely exceed 0.1 mm in diameter. These crystals are transparent and have an intense yellow color. Due to its microscopic size, it is a mineral almost exclusively accessible to specialized micromounters. ## Physical Properties Sarrochite crystals exhibit a vitreous luster. Hardness and density have not been precisely measured due to the small size and rarity of the material. It is a brittle mineral. ## Colors and Varieties This mineral occurs in a uniform, light yellow color. No color varieties or commercial forms are known. ## History and Name Sarrochite was first described in 2005 by a team of mineralogists (I. Campostrini, F. Demartin, C. M. Gramaccioli, P. Orlandi). Its name comes from the municipality of Sarroch in Sardinia (Italy), where its type locality, Punta de Su Seinargiu, is located. It was approved by the International Mineralogical Association (IMA) under number 2004-034. ## Uses Sarrochite has no industrial application. Its significance is purely scientific and as a collector's item, as a unique and complex mineral species.

Properties

Luster
Vitreous
Streak
Yellow
Transparency
Transparent
Crystal system
Trigonal

Diagnostic features

## Identification Identification of sarrochite is based on its characteristic form – small, hexagonal, tabular crystals of an intensely yellow color. Identification is practically only possible under a microscope. Final confirmation requires advanced analytical methods, such as Raman spectroscopy or X-ray diffraction (XRD). ## Distinguishing from Similar Minerals Sarrochite can be confused with other yellow secondary molybdenum minerals, such as wulfenite or molybdofornacite. However, it is distinguished by its unique, hexagonal crystal morphology (wulfenite is tetragonal) and specific occurrence environment. Precise differentiation from other rare molybdates requires specialized analysis. ## Crystal Forms This mineral forms thin, tabular crystals with a hexagonal outline. They occur as single, scattered plates on the surface of the host rock or form small, loose aggregates.

Geological environment

## Genesis Sarrochite is a secondary mineral that forms in the oxidation zones (gossans) of polymetallic deposits. Its formation is a result of the weathering of primary sulfides, mainly molybdenite, in the presence of solutions rich in calcium, phosphorus, and iron. ## Mineral Associations At its type locality, sarrochite co-occurs with minerals such as quartz, muscovite, hematite, goethite, as well as other rare molybdates, including sardignite, nuragheite, and ichnusaite. ## Localities The only confirmed and described occurrence of sarrochite in the world is its type locality: Punta de Su Seinargiu in the municipality of Sarroch, Sardinia, Italy. This is a former molybdenum mine.

Rarity

Extremely rare

For collectors

## Quality Criteria The most highly prized sarrochite specimens are those with sharply defined, well-formed, and undamaged crystals that stand out clearly from the host rock. Due to their microscopic size, crystal size is crucial – even those with a diameter of 0.1 mm are considered exceptional. Rich clusters of crystals on a small surface are also desirable. ## Popular Localities The only source of sarrochite specimens is its type locality in Sardinia. Material from this location is extremely difficult to acquire and appears on the collector's market sporadically, mainly circulating among specialists in rare minerals and micromounts.

Care and storage

## Cleaning Specimens containing sarrochite should be cleaned only with great care, using compressed air to remove dust. Any contact with water or chemicals is highly inadvisable due to potential solubility and the delicacy of the microcrystals. ## What to Avoid Contact with water, acids, bases, and other solvents must be strictly avoided. The crystals are extremely brittle and sensitive to mechanical shock. Ultrasonic cleaning devices should also be avoided. ## Storage Specimens should be stored in stable conditions, away from moisture and chemical contaminants. The safest method is storage in dedicated "micromount" boxes, which protect delicate crystals from physical damage and dust.

External references

Sources

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