Trögerite

Chemical formula: (H₃O)(U₆+O₂)(As₅+O₄)·₃H₂O

Trögerite is a rare, highly radioactive uranyl arsenate mineral, forming characteristic lemon-yellow, tabular crystals.

## Characteristics Trögerite is a hydrated uranyl arsenate belonging to the autunite group. It forms thin, tabular crystals with a square or rectangular outline, often with truncated corners. It also occurs as rosetted or fan-shaped aggregates, as well as coatings and crusts. It is a secondary mineral, formed in the oxidation zones of uranium deposits. Due to its strong radioactivity and arsenic content, trögerite specimens require specialized, safe storage. ## Physical Properties Trögerite crystals are soft and brittle, with a Mohs hardness of approximately 2-3. They exhibit a pearly luster on cleavage surfaces and a vitreous or dull luster on other faces. The mineral is transparent to translucent. Its density is about 3.3 g/cm³. Under ultraviolet light, it shows strong, yellow-green fluorescence. ## Colors and Varieties Trögerite has a characteristic lemon-yellow or canary-yellow color, sometimes with a brownish tint. It does not form named color varieties. Over time, due to dehydration (loss of water from the crystal lattice), it can transform into metatrögerite, which manifests as a loss of luster and transparency. ## History and Name The mineral was first described in 1871 by Albin Weisbach. The name comes from Richard Tröger, who was the director of the smelter at the Georg Wagsfort uranium mine in Johanngeorgenstadt, Saxony (Germany), where this mineral was discovered. ## Uses Trögerite, due to its rarity, brittleness, and high toxicity (radioactivity and arsenic), has no industrial application. It is of scientific interest only and is sought after by specialized collectors of uranium minerals.

Properties

Mohs hardness: 2-3
Luster: Pearly, Vitreous
Streak: Light yellow
Density: 3.3
Cleavage: Perfect on {001}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Tetragonal

Diagnostic features

## Identification Key diagnostic features of trögerite include its lemon-yellow color, thin-tabular crystal habit, perfect cleavage in one direction, and strong yellow-green fluorescence under UV light. It is a secondary mineral, occurring as coatings in the oxidation zones of uranium deposits. Radioactivity measurement using a Geiger counter is a primary method of field identification. ## Distinguishing from Similar Minerals Trögerite is sometimes confused with other secondary uranium minerals, such as autunite, uranophane, or zeunerite. - **Autunite** has a very similar appearance but usually crystallizes in the orthorhombic (pseudo-tetragonal) system and contains phosphorus instead of arsenic. Differentiation without chemical analysis is difficult. - **Uranophane** most often forms acicular or fibrous aggregates of a yellow color and does not have such perfect cleavage. - **Zeunerite** has a similar crystal habit, but its color is typically more green than yellow. Final differentiation often requires advanced analytical methods (XRD, EDS). ## Crystal Forms Trögerite crystallizes in the tetragonal system. It most often forms thin, square or rectangular tablets. These crystals often combine into fan-shaped, rosetted, or lamellar aggregates. It also occurs as earthy or powdery coatings on host rocks.

Geological environment

## Genesis Trögerite is a secondary mineral that forms as a result of weathering and oxidation of primary uranium minerals (mainly uraninite) in the presence of arsenic compounds. It forms under low temperature and pressure conditions, in the near-surface parts of uranium ore deposits. ## Mineral Associations This mineral often co-occurs with other secondary uranium minerals. The most common associations include: zeunerite, walpurgite, uranospinite, uraninite, arsenopyrite, nickelskutterudite, and various iron oxides (e.g., hematite). ## Localities The most important and historical occurrences of trögerite are in Germany, in the Ore Mountains (Erzgebirge) in Saxony, particularly in the Schneeberg and Johanngeorgenstadt regions (the type locality). It is also known from the Czech Republic (Jáchymov), France (deposits in the Massif Central), and several localities in the USA, including South Dakota and Utah.

Rarity

Rare

For collectors

## Quality Criteria The most valued trögerite specimens by collectors are characterized by well-formed, sharp crystals with an intense, lemon-yellow color and good transparency. Large, undamaged tablets or aesthetic, rosetted aggregates on a contrasting rock matrix fetch the highest prices. Minimal dehydration is also important – specimens with a pearly luster are more desirable than dull ones altered to metatrögerite. Due to the specific nature of the mineral, a well-documented locality is also crucial. ## Popular Localities Classic and most sought-after specimens come from historical localities in Saxony, Germany (Schneeberg, Johanngeorgenstadt). Specimens from these places have not only mineralogical but also historical value.

Care and storage

## Cleaning Trögerite specimens should generally not be wet cleaned. Only gentle dust removal with a soft brush or compressed air from a safe distance is permissible. Any contact with the mineral requires the use of protective gloves. ## What to Avoid Contact with water must be strictly avoided, as it can damage delicate crystals and lead to their disintegration. The mineral is sensitive to changes in humidity and temperature – in dry air, it dehydrates, transforming into metatrögerite. It should be protected from direct sunlight, which can accelerate the dehydration process. Avoid all chemicals, acids, and ultrasonics. Due to radioactivity and arsenic content, avoid inhaling dust and direct skin contact. ## Storage Trögerite must be stored under specialized conditions. Sealed, lead-lined or thick acrylic glass containers are recommended to limit radiation emission. The container should be clearly labeled as radioactive and toxic material. Store away from other radiation-sensitive minerals and in a place inaccessible to children and pets.

Sources

IMA Mineral List (CNMNC)