Fiemmeite
Chemical formula: Cu²⁺₂((C₂)⁶⁺O₄)(OH)₂·2H₂O
Fiemmeite is a very rare, blue organic mineral – a hydrated copper oxalate, forming microscopic, acicular crystals.
Properties
- Mohs hardness
- 2
- Color
- Sky blue
- Luster
- Vitreous
- Streak
- Pale blue
- Density
- 2.78
- Cleavage
- Almost perfect parallel to {010} or {001}
- Fracture
- Uneven
- Transparency
- Transparent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Fiemmeite is identified by its unique appearance: blue, acicular or bladed crystals forming small, radial aggregates. The key is its occurrence environment – oxidized wood in copper-rich mine deposits. Final identification requires advanced analytical methods, such as Raman spectroscopy or X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with other secondary blue copper minerals, such as chalcanthite, linarite, or azurite. Fiemmeite differs from them in crystal habit (fine, flexible needles), significantly lower hardness, and specific formation environment (oxidized plant remains). Unlike chalcanthite, it is not as readily soluble in water. ## Crystal Forms It forms elongated, bladed or acicular crystals, flattened parallel to the {010} plane. These crystals combine into radial, stellate, or chaotically arranged aggregates, and also form thin crusts.
Geological environment
## Genesis Fiemmeite is a secondary mineral of organic origin. It forms under specific conditions in the oxidation zones of copper deposits, where copper-ion-rich waters react with oxalic acid. This acid is a product of the decomposition of plant matter (e.g., fossil wood) by fungi. The mineral crystallizes directly on the surface of oxidized wood at ambient temperature. ## Mineral Associations At its type locality (Viarago mine), fiemmeite coexists with other rare oxalates, such as moolooite, wheatleyite, and lindbergite. It is also accompanied by other secondary copper minerals. ## Localities The only confirmed and described occurrence of fiemmeite in the world is its type locality: the "Viarago" mine near Scurelle in the Fiemme Valley, Trento, Italy.
Rarity
Extremely rare
For collectors
## Quality Criteria As a mineral occurring exclusively in microscopic form, the main quality criterion is the richness and aesthetics of the aggregates on the rock matrix. Specimens with clearly formed, radial rosettes of intense blue color, contrasting well with the substrate (most often decayed wood), are most valued. The size of the entire specimen is less important than the quality of the microcrystals themselves. ## Popular Localities The only source of fiemmeite specimens is its type locality in Italy. All specimens available on the collector's market come from the Viarago mine.
Care and storage
## Cleaning Fiemmeite specimens are extremely delicate and sensitive. Mechanical cleaning is not recommended. If necessary, compressed air can be used from a safe distance to remove loose dust particles. Contact with water should be avoided, as it can dissolve or damage the microscopic crystals. ## What to Avoid Contact with all chemicals, including acids and bases, must be absolutely avoided. The mineral is sensitive to elevated temperatures, which can lead to its dehydration and destruction. It should be protected from direct sunlight and humidity. ## Storage Specimens should be stored in stable conditions, in closed, padded "micromount" boxes to protect them from mechanical damage, dust, and humidity changes. It is not suitable for display in open showcases.