Fairchildite
Chemical formula: K<sub>2</sub>Ca(CO<sub>3</sub>)<sub>2</sub>
Fairchildite is a rare potassium calcium carbonate, forming microscopic, hexagonal plates, found mainly in wood ash.
Properties
- Mohs hardness
- 2.5
- Luster
- Vitreous to pearly
- Streak
- White
- Density
- 2.55
- Cleavage
- Perfect on {0001}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Hexagonal
Diagnostic features
## Identification Amateur identification of fairchildite is practically impossible due to its microscopic size and occurrence. Recognition requires specialized analytical methods, such as X-ray diffraction (XRD) or electron microprobe chemical analysis (EDS/WDS). Its origin – occurrence in wood ash – is characteristic. ## Distinguishing from similar minerals Fairchildite is chemically and structurally related to bütschliite (K₂Ca(CO₃)₂·H₂O), into which it transforms under the influence of moisture. Bütschliite crystallizes in the trigonal system, while fairchildite crystallizes in the hexagonal system. Visual distinction between these two minerals without advanced analysis is impossible. ## Crystal forms Fairchildite forms very small, thin, hexagonal crystals in the form of plates or flakes. They often occur as radial or spherulitic aggregates and rosettes.
Geological environment
## Genesis Fairchildite is a mineral with a specific genesis. It forms at high temperatures (above 600°C) as a result of the melting of potassium and calcium-rich ash from burning wood. It is a product of pyrometamorphism. In nature, its formation is associated with the burning of large amounts of biomass, for example, during forest fires, where molten ash penetrates cracks in charred trunks or rocks. ## Mineral associations This mineral co-occurs with other compounds formed under similar conditions. It is most often accompanied by bütschliite (as a product of its hydration), calcite, as well as oxides and silicates typical of wood ash. ## Localities The type locality, where the mineral was first described, is near the Grand Canyon in Arizona, USA. Other confirmed occurrences include the areas around Mayen and Pelm in the Eifel Mountains in Germany, where it is found in volcanic rocks altered by burning tree roots, and in some regions of Russia (e.g., on the Kola Peninsula).
Rarity
Very rare
For collectors
## Quality criteria The quality of fairchildite specimens is assessed primarily based on the abundance and development of microcrystals. The most valued samples are those with clearly visible, sharp, hexagonal plates forming aesthetic rosettes or dense crusts. Due to the microscopic nature of the mineral, the substrate on which it occurs is crucial – a color-contrasting substrate enhances the attractiveness of the specimen. The size of individual crystals, even if measured in tenths of a millimeter, is an important factor. ## Popular localities The most known and valued specimens by micromineral collectors come from the Eifel volcanic complex in Germany, especially from localities in the Mayen area. Specimens from there are characterized by relatively good crystal development.
Care and storage
## Cleaning Fairchildite specimens are extremely delicate and sensitive to water. They should not be cleaned wet. To remove dust, compressed air can be used very carefully from a safe distance, or a soft brush, keeping in mind the microscopic size and brittleness of the crystals. ## What to avoid Contact with water must be absolutely avoided, as it causes the mineral to decompose and transform into another compound – bütschliite. All chemicals, acids, and ultrasonic cleaners should also be avoided. The mineral is sensitive to humid air. ## Storage Fairchildite specimens must be stored in dry conditions, preferably in airtight containers (so-called "perky boxes") with a desiccant (e.g., silica gel). Due to the small size of the crystals, it is most often stored as a micromount.