Hagstromite
Chemical formula: Pb²⁺₈Cu²⁺(Te⁶⁺O₆)₂(CO₃)Cl₄
Hagstromite is an extremely rare mineral from the tellurate group, discovered in the Keystone Mine in Colorado, USA, forming tiny, hexagonal crystals.
Properties
- Mohs hardness
- 2-3
- Color
- Light yellow–green
- Luster
- Vitreous
- Streak
- Very pale yellow–green
- Density
- 7.062
- Cleavage
- Two cleavages, probably {100} and {010}
- Fracture
- Splintery
- Transparency
- Transparent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Practical identification of hagstromite is impossible without advanced analytical methods such as energy-dispersive spectroscopy (EDS) or X-ray diffraction (XRD). Preliminary identification based on visual characteristics is very difficult. It relies on finding pale blue, hexagonal, tabular crystals in association with other rare tellurates on material from the type locality (Keystone Mine). ## Distinguishing from similar minerals Based on appearance alone, hagstromite can be practically indistinguishable from other rare, blue secondary minerals such as chalcanthite, linarite, or blue tellurates and tellurites. Definitive differentiation requires specialized chemical and structural analysis. ## Crystal Forms Hagstromite crystallizes as very small, thin, hexagonal tablets, often with a six-sided outline. Crystals occur as single, isolated individuals on the host rock.
Geological environment
## Genesis Hagstromite is a secondary mineral that forms in the oxidation zones of tellurium-rich ore deposits. It originates from the weathering of primary tellurides in the presence of solutions rich in copper, lead, and chlorides. At the type locality, it occurs within altered granitic rocks. ## Mineral Associations This mineral co-occurs with other rare tellurates and tellurides. At the Keystone Mine, it has been found in association with quartz, galena, chalcopyrite, sylvanite, as well as rarer minerals such as backite, bairdite, cerussite, chlorargyrite, dugganite, emmonsite, galenobismutite, hessite, khinite, kiddcreekite, mcalpineite, parakhinite, tellurite, and xocolatlite. ## Localities The only confirmed occurrence of hagstromite in the world is its type locality – the Keystone Mine, Magnolia District, Boulder County, Colorado, USA.
Rarity
Extremely rare
For collectors
## Quality Criteria For such a rare mineral, the main criterion of value is its mere presence and confirmed identity. Specimens are most highly valued when hagstromite crystals, despite their microscopic size, are well-formed, have a distinct pale blue color, and are embedded on an aesthetically pleasing rock matrix. A rich association with other rare minerals is also important. ## Popular Localities The only source of hagstromite specimens is the Keystone Mine in Colorado, USA. All specimens available on the collector's market originate from this single locality.
Care and storage
## Cleaning Hagstromite specimens, due to their microscopic size and delicacy, generally should not be cleaned mechanically or chemically. If cleaning is absolutely necessary, compressed air can be carefully used (from a safe distance) to remove loose dust. Contact with water and any chemicals should be avoided. ## What to avoid Contact with acids, detergents, and other chemical agents must be strictly avoided. The mineral is potentially sensitive to changes in temperature and humidity. It should not be exposed to direct sunlight. ## Storage Hagstromite specimens should be stored under stable conditions, in specialized micromount boxes that protect them from dust, mechanical damage, and sudden environmental changes. Storage in a dry place is crucial.