Tombstoneite
Chemical formula: (Ca₀.₅Pb²⁺₀.₅)Pb²⁺₃Cu²⁺₆Te⁶⁺₂O₆(Te⁴⁺O₃)₆(Se⁴⁺O₃)₂(S⁶⁺O₄)₂·3H₂O
Tombstoneite is an extremely rare, complex lead, copper, and calcium tellurite-selenite-sulfate, forming microscopic, tabular, green crystals.
Properties
- Color
- Green
- Luster
- Vitreous
- Streak
- Pale green
- Density
- 5.680
- Cleavage
- on {001}
- Fracture
- Irregular/Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Trigonal
Diagnostic features
## Identification Identification of tombstoneite is only possible using advanced analytical methods, such as Raman spectroscopy or chemical analysis with an electron microprobe (EDS/WDS). In collector conditions, identification relies on the green color, the characteristic form of microscopic, tabular crystals forming rosette aggregates, and knowledge of co-occurring minerals from the type locality (Tombstone, Arizona). ## Distinguishing from Similar Minerals It can be confused with other secondary, green copper minerals, such as brochantite, malachite, and especially with other rare tellurites and selenites from the same locality (e.g., quetzalcoatlite, oboyerite). Definitive differentiation requires specialized studies, as visually these minerals can be identical in the form of microscopic coatings. ## Crystal Forms Crystals are very small, thin, and tabular, with a hexagonal outline. They typically form rosettes, spherulitic or radial aggregates, as well as thin coatings on the rock.
Geological environment
## Genesis Tombstoneite is a secondary mineral, forming in the oxidation (weathering) zone of polymetallic ore deposits. It forms as a result of the alteration of primary minerals containing tellurium, selenium, copper, and lead under conditions of low temperature and pressure, in the presence of sulfate-rich waters. ## Mineral Associations At the type locality (Tombstone, Arizona), it co-occurs with many other rare secondary minerals, such as: quetzalcoatlite, oboyerite, graemite, xocomecatlite, eztlite, jaszczakite, as well as more common minerals like quartz, barite, galena, chalcopyrite, and pyrite. ## Localities The only confirmed occurrence of tombstoneite in the world is its type locality – the historic Tombstone mining district in Cochise County, Arizona, USA. Specimens come from the dumps of old mines, such as Joe, Grand Central, and Toughnut.
Rarity
Extremely rare
For collectors
## Quality Criteria As a "micromount" mineral, specimens with clearly formed, sharp crystals creating aesthetic, rosette-like aggregates are most highly valued. Good color contrast with the substrate (rock matrix) and a rich association with other rare minerals are important. The size of the aggregates, although still microscopic, also affects value – larger and denser clusters are more desirable. ## Popular Localities The only source of specimens is the historic Tombstone mining district in Arizona (USA). The best specimens, from which research material was obtained, were collected from the dumps of the Joe, Grand Central, and Toughnut mines.
Care and storage
## Cleaning Due to the extreme rarity and fragility of specimens, mechanical cleaning is absolutely inadvisable. Any attempts to use brushes, water, or compressed air can irreversibly damage the microscopic crystals. Specimens should be left in their untouched state. ## What to Avoid Contact with any chemicals, including acids and bases, should be avoided. The mineral is likely sensitive to changes in temperature and humidity. It should be protected from direct sunlight, which can cause fading. Vibrations and shocks can lead to the crumbling of delicate aggregates. ## Storage Tombstoneite specimens should only be stored in specialized, sealed "micromount" boxes that protect them from dust, mechanical damage, and humidity changes. The box should be kept in a stable environment, away from sources of heat and light.