Pertlikite
Chemical formula: K<sub>2</sub>(Fe<sup>2+</sup>,Mg)<sub>2</sub>(Mg,Fe<sup>3+</sup>)<sub>4</sub>Fe<sup>3+</sup><sub>2</sub>Al(S<sup>6+</sup>O<sub>4</sub>)<sub>12</sub>·18H<sub>2</sub>O
Pertlikite is an extremely rare, hydrated sulfate of potassium, iron, magnesium, and aluminum, forming tiny, yellow crystals.
Properties
- Mohs hardness
- 2.5
- Luster
- Vitreous
- Streak
- Pale yellow
- Density
- 2.81
- Cleavage
- None
- Transparency
- Transparent
- Crystal system
- Trigonal
Diagnostic features
## Identification Pertlikite is identified by its characteristic yellow color, occurrence as microscopic, tabular crystals, and specific geological environment (mine dumps). A key diagnostic feature is its co-occurrence with other rare secondary sulfates, such as voltaite, rhomboclase, or fibroferrite. It is very soft and water-soluble. ## Distinguishing from Similar Minerals Pertlikite can be confused with other yellow secondary sulfates with which it often co-occurs. It is distinguished from *jarosite* by its crystal habit (jarosite more often forms earthy aggregates or microscopic, shiny flakes) and slightly lower hardness. *Copiapite* can be more greenish-yellow and forms scaly aggregates. Certain identification is almost exclusively possible using advanced analytical methods, such as X-ray diffraction (XRD) or chemical microanalysis (EDS/WDS). ## Crystal Forms It forms aggregates of small, tabular or equant (isometric) crystals with trigonal symmetry. The size of individual crystals rarely exceeds 0.2 mm.
Geological environment
## Genesis Pertlikite is a secondary mineral, forming under specific conditions on mine dumps. Its genesis is related to the weathering (oxidation) processes of iron sulfides (mainly pyrite) in an arid climate. Its formation requires the presence of aluminum and potassium, likely originating from weathering clay minerals or feldspars present in the gangue. ## Mineral Associations This mineral occurs in association with other secondary sulfates, such as voltaite, copiapite, jarosite, fibroferrite, rhomboclase, and halotrichite. ## Localities The only confirmed occurrence of pertlikite in the world is its type locality – the dump of the former "Adolf" coal and pyrite mine in Běloves (part of the town of Náchod), in the Hradec Králové Region, Czech Republic.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of pertlikite specimens, being a micromineral, is primarily assessed based on the richness of aggregates and the size of the crystals, even if they are sub-millimeter. The most prized samples are those with well-formed, shiny crystals forming dense aggregates on a small rock matrix. The presence of other rare associated minerals on the same specimen adds additional value. ## Popular Localities Pertlikite specimens originate exclusively from one location in the world – the "Adolf" mine dump in the Czech Republic. Material from this locality is extremely difficult to obtain and is a rarity in specialized micromineral collections.
Care and storage
## Cleaning Pertlikite specimens are extremely sensitive to water and moisture. Cleaning should only be done dry, using a very soft brush to remove dust or compressed air from a safe distance to avoid damaging the fragile crystals. ## What to Avoid Contact with water and other liquids, which can dissolve the mineral, must be strictly avoided. High air humidity is also harmful and can lead to its slow decomposition. The mineral is very soft (hardness 2.5), so it must be protected from any friction and contact with harder objects. High temperatures should also be avoided, as they can cause the loss of crystallization water and destruction of the structure. ## Storage Pertlikite must be stored in conditions of controlled, low humidity. The best solution is to place the specimen in a sealed, airtight box (a "perky box") along with a desiccant, such as silica gel.