Fukalite
Chemical formula: Ca<sub>4</sub>Si<sub>2</sub>O<sub>6</sub>(CO<sub>3</sub>)(OH)<sub>2</sub>
A rare calcium silicate, white or pink in color, found in skarns in Japan, valued by collectors for its unique parageneses.
Properties
- Mohs hardness
- 4.5
- Luster
- Vitreous to Pearly
- Streak
- White
- Density
- 2.73
- Cleavage
- Perfect on {010}, Good on {100}
- Fracture
- Uneven
- Transparency
- Translucent to Opaque
- Crystal system
- Monoclinic
Diagnostic features
## Identification Fukalite is identified based on its specific occurrence environment (skarns), relatively low hardness, and characteristic mineral associations such as wollastonite, gehlenite, or spurrite. Its white or pinkish color and fibrous appearance are also helpful. Reaction with dilute hydrochloric acid (due to the presence of a carbonate group) can be a diagnostic feature, but it should be performed with utmost caution on a small fragment. ## Distinguishing from Similar Minerals It can be confused with other white skarn minerals such as wollastonite, tremolite, or xonotlite. Wollastonite is harder (4.5-5) and has a different crystal habit. Tremolite is harder (5-6) and has perfect cleavage. Final distinction often requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms Fukalite crystallizes in the monoclinic system. It forms very small, bladed or acicular crystals, most often occurring as felted, fibrous, or radial aggregates. Granular aggregates are less common.
Geological environment
## Genesis Fukalite is a mineral of metamorphic origin. It forms in contact zones between igneous rock intrusions and carbonate rocks (limestones or dolomites). It is a typical component of high-temperature calcium-silicate skarns. ## Mineral Associations This mineral often co-occurs with other skarn minerals such as wollastonite, gehlenite, spurrite, tilleyite, cuspidine, calcite, as well as various garnets (grossular, andradite) and vesuvianite. ## Localities The most important and classic occurrence of fukalite is its type locality – the Fuka mine, near Takahashi City, Okayama Prefecture on Honshu Island, Japan. This is the main source of the best-formed specimens of this mineral. It is also known from several other skarn localities worldwide, but remains a very rare mineral.
Rarity
Very rare
For collectors
## Quality Criteria The most valued by collectors are specimens with clearly visible, rich aggregates of fukalite, preferably with a pink coloration. Key is the association with other rare skarn minerals, such as spurrite or tilleyite, forming aesthetic and scientifically interesting parageneses. Specimens from the type locality (Fuka, Japan) are particularly sought after. ## Popular Localities The only commercially significant and known source of collectible fukalite specimens is the Fuka mine in Japan. Specimens from this location set the standard for this mineral.
Care and storage
## Cleaning Fukalite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to possible reactivity with acids, all chemical cleaning agents should be avoided. If water is necessary, it should be distilled water, and the specimen should be dried quickly and thoroughly. ## What to Avoid Avoid contact with acids, which can react with the carbonate groups in the mineral's structure, leading to damage. Fukalite is relatively soft, so it must be protected from scratching by harder minerals. Ultrasonic cleaners should also be avoided. ## Storage It is recommended to store fukalite specimens in separate, padded boxes to prevent abrasions and scratches. It should be protected from dust and chemical contaminants.