Lonecreekite

Chemical formula: N₃-H₄Fe₃+(S₆+O₄)₂·₁₂H₂O

Lonecreekite is a rare, hydrated ammonium iron sulfate, forming small, colorless or pale yellow crystals, most commonly found in coal mines.

## Characteristics Lonecreekite is a mineral from the alunite group, chemically classified as a hydrated ammonium iron sulfate. It occurs as small, tabular or octahedral crystals, often forming granular aggregates or efflorescences. It is a secondary mineral, formed under specific conditions, usually as a result of the weathering of iron sulfides (such as pyrite) in the presence of organic matter providing ammonia. ## Physical Properties Lonecreekite crystals are brittle and characterized by a vitreous luster. This mineral is relatively soft, and its density is low, which is typical for hydrated sulfates. It is soluble in water. ## Colors and Varieties Lonecreekite is usually colorless, white, or pale yellow. Its color depends on its purity and the presence of impurities. No named varieties are distinguished. ## History and Name The mineral's name comes from its discovery site in 1962 – Lone Creek Falls, near Sabie in the Mpumalanga province (formerly Transvaal) in the Republic of South Africa. It was described by J.E. de Villiers. ## Uses Lonecreekite has no industrial significance. It is solely an object of interest for collectors specializing in rare minerals and scientists studying the weathering processes of sulfide minerals.

Properties

Mohs hardness: 2-2.5
Luster: Vitreous
Streak: White
Density: 1.89
Cleavage: None
Fracture: Conchoidal
Transparency: Transparent
Crystal system: Cubic

Diagnostic features

## Identification Lonecreekite is primarily identified based on its specific occurrence environment (coal mines, slag heaps, weathering pyritiferous shales) and physical properties. Key features include low hardness, water solubility, vitreous luster, and characteristic small crystals. A chemical reaction confirming the presence of ammonium and iron ions is the ultimate proof. ## Distinguishing from Similar Minerals It can be confused with other secondary sulfates, such as tschermigite (ammonium aluminum sulfate) or other minerals from the alunite group. Distinguishing it from tschermigite often requires chemical analysis to confirm the presence of iron instead of aluminum. Many similar sulfates form under the same conditions, which further complicates visual identification. ## Crystal Forms Lonecreekite crystals are usually small, tabular or isometric, often taking the form of octahedra. It also forms granular aggregates, powdery efflorescences, and crusts on rock surfaces.

Geological environment

## Genesis Lonecreekite is a secondary mineral. It forms as a result of the oxidation of sulfide minerals (mainly pyrite and marcasite) in an ammonia-rich environment. This ammonia most often comes from the decomposition of organic matter, which is why typical formation sites for lonecreekite include burning mine dumps, weathering bituminous shales, and cave deposits rich in guano. ## Mineral Associations It often co-occurs with other secondary sulfates, such as tschermigite, gypsum, melanterite, epsomite, as well as native sulfur and pyrite. ## Localities The most important lonecreekite localities worldwide include: - Lone Creek Falls near Sabie, Mpumalanga (RSA) - type locality. - Anna Mine in Alsdorf, North Rhine-Westphalia (Germany). - Burning coal dumps in Pennsylvania (USA), e.g., in Northumberland County. - Hungarian mines, including those near Pécs and Tatabánya.

Rarity

Rare

For collectors

## Quality Criteria The collector appeal of lonecreekite specimens primarily depends on the crystal habit and size. Well-formed, transparent, isometric crystals, clearly distinct from the host rock, are most valued. Due to the mineral's instability, well-preserved specimens that have not undergone dehydration or disintegration are rare and sought after. Crystal size rarely exceeds a few millimeters. ## Popular Localities Specimens from the classic locality in South Africa are rare on the market. Most available collector specimens come from burning coal dumps in Pennsylvania (USA) and from some mines in Germany and Hungary.

Care and storage

## Cleaning Lonecreekite specimens are very sensitive to water, in which they dissolve. Mechanical cleaning is the only permissible method and must be carried out with extreme caution, dry, using a very soft brush to remove dust. ## What to Avoid Contact with water and all liquids must be strictly avoided. The mineral is hygroscopic, meaning it absorbs moisture from the air, which can lead to its slow disintegration. It should be protected from high humidity, direct sunlight, and temperature changes. ## Storage Lonecreekite requires storage in conditions of controlled, low humidity. It is best kept in a sealed, airtight container (a "perky box") with a desiccant (e.g., silica gel). Exposure to open air is not recommended.

Sources

IMA Mineral List (CNMNC)