Numanoite
Chemical formula: Ca₄Cu²⁺B₄O₆(OH)₆(CO₃)₂
Numanoite is a very rare, blue copper and calcium borate, forming microscopic, prismatic crystals in skarns.
Properties
- Mohs hardness
- 4.5
- Color
- bluish green
- Luster
- Vitreous
- Streak
- Light blue
- Density
- 2.96
- Cleavage
- {100} {110}
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Numanoite can be identified by its characteristic light blue color, vitreous luster, and form of small, prismatic crystals forming radial aggregates. It occurs in a specific geological environment – calc-silicate skarns. Final identification requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS). ## Distinguishing from Similar Minerals Numanoite can be confused with other blue secondary copper minerals, such as azurite, but it typically forms much smaller crystals. At its locality of occurrence (Fuka mine), it co-occurs with takimotoite, which has a similar composition but crystallizes in the monoclinic system and has a darker, blue-green color. Distinguishing it from other rare copper borates is impossible without specialized equipment. ## Crystal Forms Numanoite crystals are elongated, prismatic, with a cross-section close to square. They usually occur in the form of radial or tangled aggregates, as well as single, overgrown crystals on the surface of the host rock.
Geological environment
## Genesis Numanoite is a secondary mineral, formed in the contact zone (skarn) between a granodiorite intrusion and carbonate rocks (limestones). Its formation is associated with hydrothermal and metasomatic processes, where boron- and copper-rich solutions reacted with calcareous rocks. ## Mineral Associations This mineral co-occurs with other borates and skarn minerals. At the type locality (Fuka mine), it was found in association with minerals such as: takimotoite, olshanskyite, nifontovite, borcarite, siberite, calcite, gehlenite, wollastonite, and garnets from the grossular-andradite group. ## Localities The only confirmed and described occurrence of numanoite in the world is its type locality – the Fuka mine, near Takahashi City, Okayama Prefecture, Japan.
Rarity
Extremely rare
For collectors
## Quality Criteria The quality of numanoite specimens is primarily assessed based on the richness and aesthetics of microcrystal aggregates on the rock matrix. The most prized specimens are those with clearly formed, radial clusters of intense, light blue color, contrasting well with the substrate. Due to their microscopic nature, the size of individual crystals is not a key criterion; rather, the overall appearance of the aggregate matters. ## Popular Localities The only source of numanoite specimens is the Fuka mine in Japan. Material from this locality is extremely rare and sought after by collectors specializing in rare minerals and "micromount" specimens.
Care and storage
## Cleaning Numanoite specimens are extremely delicate and usually occur as microscopic crystals on a rock matrix. Mechanical or chemical cleaning is not recommended. Any attempts at cleaning may irreversibly destroy the fragile mineral structure. If dust removal is necessary, a gentle stream of compressed air can be used from a safe distance. ## What to Avoid Contact with water, acids, bases, and other chemicals should be strictly avoided, as numanoite, being a carbonate, is susceptible to chemical reactions. It should be protected from ultrasound, high temperatures, and sudden temperature changes. Due to its microscopic nature, any vibrations and shocks should be avoided. ## Storage Specimens should be stored under stable conditions, in closed, padded "micromount" boxes that protect against dust, moisture, and mechanical damage. Store away from heat sources and direct sunlight.