Swartzite

Chemical formula: CaMg(U<sup>6+</sup>O<sub>2</sub>)(CO<sub>3</sub>)<sub>3</sub>·12H<sub>2</sub>O

Swartzite is a rare, secondary uranyl mineral, forming bright yellow, fluorescent coatings and aggregates of fine crystals.

## Characteristics Swartzite is a hydrated calcium, magnesium, and uranyl carbonate. It occurs as aggregates of very small, platy or acicular crystals, which rarely reach a size visible to the naked eye. It also forms coatings and crusts on host rocks. Its most characteristic features are its intensely bright yellow to yellowish-green color and strong fluorescence under ultraviolet light. ## Physical Properties Swartzite crystals are very small and brittle. This mineral exhibits a vitreous luster. It is transparent to translucent. Due to the presence of uranium, it is a radioactive mineral and requires careful handling. ## Colors and Varieties Swartzite occurs in a characteristic, bright yellow or greenish-yellow color. No color varieties or commercial varieties are distinguished. ## History and Name The mineral is named in honor of Charles Kephart Swartz (1861-1949), a professor of geology at Johns Hopkins University. It was first described in 1947 based on samples found at Hillside, Yavapai County, Arizona, USA. ## Uses Due to its rarity and small crystal size, swartzite has no industrial applications. It is solely an object of interest for collectors specializing in uranium minerals and rare mineral species.

Properties

Mohs hardness
3
Luster
Vitreous
Streak
Light yellow
Density
2.3
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification The key diagnostic feature of swartzite is its intense, bright yellow to greenish-yellow fluorescence under ultraviolet light (both shortwave and longwave). Small, acicular or platy crystals forming coatings and aggregates are also characteristic. It reacts with acids, releasing carbon dioxide bubbles. ## Distinguishing from Similar Minerals Swartzite can be confused with other secondary uranium minerals of similar color, such as andersonite, liebigite, or bayleyite. Andersonite crystallizes in the trigonal system and has a slightly different fluorescence (blue-green). Liebigite and bayleyite have very similar appearances and properties, and their definitive distinction often requires advanced analytical methods, such as X-ray diffraction (XRD). Swartzite is distinguished from them by its monoclinic crystallization. ## Crystal Forms Swartzite forms very small, elongated, platy or acicular crystals, usually grouped into radial aggregates, rosettes, or forming thin coatings and crusts on rock surfaces.

Geological environment

## Genesis Swartzite is a secondary mineral, forming in the oxidation zones of uranium deposits. It forms as a result of carbonate-rich waters acting on earlier uranium minerals. It most often occurs as coatings and crusts on the walls of mine workings in uranium mines. ## Mineral Associations It often co-occurs with other secondary uranium minerals, such as andersonite, bayleyite, liebigite, schröckingerite, as well as with gypsum and calcite. ## Localities The most important and classic localities for this mineral are mines in Utah (USA), especially the Hillside mine in Arizona (type locality), the Delta mine (formerly MESA), and the Lucky Strike mine in the San Rafael district. It is also known from uranium mines in the Czech Republic (e.g., Jáchymov) and other places worldwide where uranium deposits occur in sedimentary rocks.

Rarity

Rare

For collectors

## Quality Criteria Specimens with well-formed, though still microscopic, crystals forming rich, rosette-like or radial aggregates are most valued by collectors. The intensity and saturation of the bright yellow color also increase the specimen's value. Aesthetic composition on the host rock and strong, effective fluorescence under UV light are also important. ## Popular Localities Specimens from mines in the San Rafael district, Utah (USA), are considered classic and most desired by collectors specializing in uranium minerals.

Care and storage

## Cleaning Swartzite specimens should generally not be wet cleaned. The fine, acicular crystals are extremely delicate and can be easily damaged. If cleaning is absolutely necessary, compressed air (from a safe distance) can be used to remove dust. ## What to Avoid Avoid contact with water and chemicals. As a secondary mineral, it is soluble in acids. It should be protected from shocks, impacts, and abrasion. Due to its uranium content, exposure should be limited, and hands should always be washed after contact with the mineral. Do not store in bedrooms or areas of constant human presence. ## Storage Swartzite specimens should be stored in closed, stable containers (e.g., "perky boxes") to protect them from mechanical damage and dust. Due to radioactivity, it is recommended to store them in a location away from constant human presence, preferably as part of a larger collection of radioactive minerals, with appropriate labeling.

Sources

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