Frankhawthorneite
Chemical formula: Cu<sup>2+</sup><sub>2</sub>Te<sup>6+</sup>O<sub>4</sub>(OH)<sub>2</sub>
Frankhawthorneite is a very rare copper hydroxy-tellurate, forming microscopic, platy crystals of an intensely green color.
Properties
- Mohs hardness
- 3-4
- Luster
- Vitreous
- Streak
- Light green
- Density
- 5.16
- Cleavage
- Perfect on {001}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Frankhawthorneite can be identified by its characteristic, intense emerald-green color, platy crystal habit, and occurrence as small, rosette-like aggregates. Its origin from the oxidation zones of deposits containing tellurides and copper minerals is also key. ## Distinguishing from Similar Minerals It can be confused with other secondary copper minerals of green color, such as brochantite, malachite, or euchroite. Differentiation requires advanced research methods, such as chemical analysis (EDS) to confirm the presence of tellurium and copper, and X-ray diffraction (XRD) to identify the crystal structure. Visually, it is distinguished by its crystal form and specific shade of green. ## Crystal Forms Crystals are very small, thin, and platy, with a hexagonal outline. They typically form radial or rosette-like aggregates, as well as thin crusts and coatings on the host rock.
Geological environment
## Genesis Frankhawthorneite is a secondary mineral, formed in the oxidation zones of hydrothermal ore deposits rich in tellurium and copper. It forms as a result of the weathering of primary tellurides and copper sulfides under conditions of low temperatures and pressures. ## Mineral Associations It most commonly co-occurs with other secondary copper and tellurium minerals. In the type locality (Centennial Eureka Mine), it was found in association with quartz, barite, enargite, as well as rarer tellurates and tellurites, such as jensenite, leisingite, cesbronite, and eztatalite. ## Localities This is an extremely rare mineral, known from only a few locations worldwide. Besides the type locality at the Centennial Eureka Mine in Utah (USA), its occurrence has also been confirmed at the Bambolla Mine in Moctezuma, Sonora State, Mexico.
Rarity
Very rare
For collectors
## Quality Criteria The most highly valued specimens are those with well-formed, sharply terminated crystals forming aesthetic, radial aggregates. The intensity and purity of the emerald-green color are crucial. Due to the microscopic nature of the mineral, the size of the aggregates is also important – the larger and richer in crystals the druse, the more valuable the specimen. Contrast with light host rock (e.g., quartz) also enhances visual appeal. ## Popular Localities By far the most known and prized specimens come from the type locality – the Centennial Eureka Mine in Utah, USA. Specimens from the Mexican Bambolla Mine are also sought after, but the American finds are considered classic for this species.
Care and storage
## Cleaning Specimens should be cleaned very carefully, using compressed air to remove dust. Due to the extreme delicacy and small size of the crystals, contact with water or a brush is highly risky and can lead to the destruction of the specimen. ## What to Avoid Avoid contact with all chemicals, including acids and detergents. The mineral is brittle and sensitive to ultrasound and sudden temperature changes. It should not be exposed to direct sunlight, which can cause it to fade. ## Storage Frankhawthorneite specimens, as microminerals, should be stored in specialized, sealed boxes (micromount type) that protect them from dust, mechanical damage, and moisture. Display should only be done under a microscope.