Heinrichite

Chemical formula: Ba(U⁶⁺O₂)₂(As⁵⁺O₄)₂·₁₀H₂O

Heinrichite is a rare, radioactive mineral from the autunite group, distinguished by its intense, yellowish-green color and tabular crystals.

## Characteristics Heinrichite is a hydrated uranyl arsenate of barium, belonging to the autunite group. It forms characteristic, thin, tabular crystals with a square or octagonal outline, often aggregated into fan-like or nearly parallel clusters. Specimens usually have an intense, yellowish-green or green color, resembling the related autunite or torbernite in appearance. Due to its uranium content, this mineral is highly radioactive and exhibits intense, green fluorescence under ultraviolet light (both shortwave and longwave). ## Physical Properties Heinrichite crystals are soft and brittle, with a Mohs hardness of approximately 2.5. They have a vitreous luster, and a pearly luster on cleavage surfaces. They are transparent to translucent. The mineral's density is about 3.36 g/cm³. Like other minerals in this group, it can undergo dehydration, leading to the formation of metaheinrichite and a change in physical properties, including optical ones. ## Colors and Varieties Heinrichite occurs in shades from pale green, through yellowish-green, to intense green. No named varieties are distinguished. Differences in color saturation depend mainly on crystallization conditions and the degree of hydration. ## History and Name The mineral was first described in 1958 by E. Wm. Heinrich, after whom it is named. The discovery was made on material from Goose Lake in Lake County, Oregon, USA. Analyses confirmed it to be a new mineral of the autunite group, in which barium is the dominant cation. ## Uses Heinrichite has no industrial application. Due to its rarity, attractive color, crystal form, and strong fluorescence, it is a prized collector's mineral. Its high radioactivity also makes it significant for scientists studying uranium minerals.

Properties

Mohs hardness: 2.5
Luster: Vitreous, Pearly
Streak: Light green
Density: 0
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification The most important diagnostic features of heinrichite are its characteristic yellowish-green color, thin-tabular crystal form with a square outline, and very strong, green fluorescence under UV light. Its high radioactivity, easily detectable with a Geiger counter, is also crucial. It is also distinguished by excellent cleavage in one direction. ## Distinguishing from Similar Minerals - **Autunite and meta-autunite:** Have a very similar appearance and fluorescence, but contain calcium instead of barium. Differentiation requires chemical analysis (EDS/WDS). - **Torbernite and metatorbernite:** Have a similar crystal form, but usually a more intense green color and contain copper instead of barium. They do not exhibit fluorescence under UV light. - **Uranocircite and metauranocircite:** These are barium-uranium phosphates (not arsenates) and have a very similar appearance. Final differentiation is only possible through chemical analysis. - **Zeunerite and metazeunerite:** These are uranyl arsenates of copper. They have a similar form but contain copper, not barium, and do not fluoresce. ## Crystal Forms Heinrichite crystallizes in the form of thin, square or octagonal tablets. Crystals often form fan-like, rosette-like, or nearly parallel packets and aggregates. It also occurs as scaly coatings and clusters on the host rock.

Geological environment

## Genesis Heinrichite is a secondary uranium mineral, forming in the oxidation (weathering) zones of uranium deposits containing arsenic. It forms as a result of the interaction of barium-rich waters with primary uranium minerals, such as uraninite, in the presence of arsenic (e.g., from the oxidation of arsenopyrite). It is a relatively low-temperature mineral. ## Mineral Associations This mineral often co-occurs with other secondary uranium minerals, such as nováčekite, kahlerite, uraninite, zeunerite, torbernite, uranophane, as well as with arsenopyrite, realgar, orpiment, fluorite, and quartz. ## Localities The most important and classic localities for this mineral are: - **USA:** Goose Lake area in Lake County, Oregon (type locality). - **Germany:** Mines in the Wittichen and Badenweiler areas in the Black Forest (Baden-Württemberg), where some of the world's best specimens were found; and also in the Schneeberg area in Saxony. - **France:** Various deposits in the Massif Central. - **Italy:** Val Rendena in Trentino. - **Czech Republic:** Jáchymov.

Rarity

Rare

For collectors

## Quality Criteria The most prized heinrichite specimens are characterized by sharply defined, well-formed crystals of intense, yellowish-green color. Aggregates of crystals forming aesthetic fans or rosettes, set on a contrasting rock matrix, are highly valued. The transparency and luster of the crystals are also important. Specimens from classic localities, such as the Black Forest in Germany, are particularly sought after by collectors of uranium minerals. ## Popular Localities For collectors, specimens from the historic mines in the Black Forest, Germany (e.g., Sophia mine in Wittichen), which yielded specimens of exceptional aesthetics, are most desirable. Material from the type locality in Oregon (USA) also holds historical value.

Care and storage

## Cleaning Heinrichite specimens are extremely delicate, brittle, and sensitive to dehydration. Cleaning should be kept to an absolute minimum. If necessary, a very soft brush can be used to remove dust. Avoid contact with water, which can damage the crystals and alter their chemical composition. ## What to Avoid - **Water and Chemicals:** Absolutely avoid contact with water, acids, and other cleaning agents. - **High Temperature and Dry Air:** Storage in overly dry or warm conditions causes water loss from the crystal lattice and transformation into metaheinrichite. This leads to a loss of transparency and cracking of crystals. - **Sunlight:** Prolonged exposure to direct sunlight can cause fading and accelerate the dehydration process. - **Vibrations and Impacts:** The mineral is very brittle, and its crystals are easily susceptible to mechanical damage. ## Storage It is recommended to store specimens in sealed, transparent containers (e.g., "perky boxes"), which help maintain a stable humidity level and protect against physical damage. Due to its strong radioactivity, specimens should be stored away from areas of constant human presence, in specially marked containers, and away from other radiation-sensitive minerals.