Eurekadumpite
Chemical formula: (Cu<sup>2+</sup>,Zn<sup>2+</sup>)<sub>16</sub>(Te<sup>4+</sup>O<sub>3</sub>)<sub>2</sub>(As<sup>5+</sup>O<sub>4</sub>)<sub>3</sub>Cl(OH)<sub>18</sub>·7H<sub>2</sub>O
Eurekadumpite is a very rare, secondary copper and zinc mineral with a bright, greenish-yellow color, discovered on the dump of the Eureka mine in Utah, USA.
Properties
- Mohs hardness
- ~3
- Luster
- Vitreous
- Streak
- Light greenish-yellow
- Density
- 3.86
- Cleavage
- Good on {010}
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Eurekadumpite can be identified by its unique, bright greenish-yellow color, acicular or prismatic crystal habit forming radial aggregates, and by its extreme rarity and occurrence in a specific environment. Final identification requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS). ## Distinguishing from Similar Minerals It can be confused with other secondary, brightly colored arsenic or tellurium minerals. It is distinguished from the visually similar *eurekadumpite-Zn* (later renamed haynesite-Zn) by its chemical composition. From other green copper arsenates, such as annabergite or olivenite, it differs by the presence of tellurium, which can only be determined by chemical analysis. ## Crystal Forms Crystals are prismatic to acicular, often flattened. They typically form radial, stellate, or tangled aggregates. Single, well-formed crystals are extremely rare.
Geological environment
## Genesis Eurekadumpite is a secondary mineral that forms in the oxidation zones of polymetallic deposits rich in copper, zinc, arsenic, and tellurium. It originates from the weathering of primary ores (mainly sulfides and tellurides) under low temperature and pressure conditions, on mine dumps or in the near-surface parts of the deposit. ## Mineral Associations This mineral co-occurs with other rare secondary minerals. In its type locality, it was found in association with quartz, barite, gypsum, jarosite, emmonsite, mcalpineite, frankhawthorneite, jensenite, ottoite, and tellurite. ## Localities The only confirmed occurrence of eurekadumpite in the world is its type locality: the dump of the Centennial Eureka mine, in the Tintic district, Juab County, Utah, USA.
Rarity
Extremely rare
For collectors
## Quality Criteria The most prized specimens are those with rich, dense clusters of well-formed, radial aggregates of intense, greenish-yellow color. Contrast with the darker matrix also enhances visual and collector value. Due to the microscopic nature of the mineral, the overall size of the specimen is less important than the quality and abundance of the crystals themselves. ## Popular Localities The only source of specimens is the Centennial Eureka mine in Utah, USA. Material from this location is extremely limited, and new finds are very unlikely.
Care and storage
## Cleaning Specimens should only be cleaned with compressed air to remove dust. Due to extreme delicacy and potential water solubility, any contact with liquids, including water or alcohol, should be avoided. The use of brushes is excluded, as it would destroy the fragile crystals. ## What to Avoid Contact with water and other chemicals must be strictly avoided. The mineral is very fragile, so it should be protected from vibrations, impacts, and abrasions. It should not be exposed to ultrasound. Store away from heat sources. ## Storage It is recommended to store specimens exclusively in sealed, lockable "micromount" boxes, which protect against dust, moisture, and mechanical damage. Eurekadumpite is typically a microscopic mineral, so exposure outside such a box is not practiced.