Haiweeite

Chemical formula: Ca(U₆+O₂)₂Si₅O₁₂(OH)₂·₆H₂O

A rare secondary mineral from the uranyl silicate group, forming characteristic acicular crystals of intense yellow color and strong fluorescence.

## Characteristics Haiweeite is a hydrated calcium uranyl silicate, belonging to the secondary minerals of the oxidation zones of uranium deposits. It forms characteristic, fine, acicular or fibrous crystals, which often arrange themselves into radial aggregates, rosettes, and crusts. Its appearance is very typical of many secondary uranium minerals, with which it is often confused. ## Physical Properties Haiweeite crystals are brittle and delicate. The mineral's Mohs hardness is approximately 3.5. It exhibits a vitreous luster, and in the case of fine-fibrous aggregates, a silky luster. It is a transparent to translucent mineral. ## Colors and Varieties Haiweeite occurs in shades from canary yellow and lemon yellow to yellowish-green. Its color is intense and is one of its main diagnostic features. No color varieties or commercial varieties are distinguished. ## History and Name The mineral's name comes from its discovery locality – the vicinity of Haiwee Reservoir in the Coso Mountains, Inyo County, California (USA). It was first described in 1959 by T. C. McBurney and Joseph Murdoch. ## Uses Due to its rarity and small accumulations, haiweeite has no industrial application. However, it is a valued and sought-after collector's mineral, especially specimens with well-formed crystals and intense color.

Properties

Mohs hardness: 3.5
Luster: Vitreous to Silky
Streak: Pale yellow
Density: 3.33
Cleavage: Good on {010}
Fracture: Uneven
Transparency: Transparent to Translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification The most important diagnostic features of haiweeite are its intense yellow color, acicular crystal habit forming radial aggregates, and strong, bright green fluorescence under ultraviolet light (both shortwave and longwave). A definitive feature is its radioactivity, which can be easily detected with a Geiger counter. ## Distinguishing from Similar Minerals Haiweeite is visually very similar to other secondary uranyl minerals. It can be confused with: - **Uranophane**: often has a more fibrous habit and a slightly different, weaker, or yellowish-green fluorescence. - **Boltwoodite**: can be almost identical, and definitive distinction often requires advanced studies, e.g., X-ray diffraction (XRD). - **Carnotite**: usually forms earthy or powdery coatings, not distinct acicular crystals. ## Crystal Forms Haiweeite crystallizes in the form of very fine, elongated, acicular crystals. Most often, they occur as radial aggregates resembling hedgehogs or fans, as well as crusts and coatings on the host rock.

Geological environment

## Genesis Haiweeite is a secondary mineral, forming in the oxidation (weathering) zones of uranium deposits. It forms as a result of the alteration of primary uranium minerals, such as uraninite, under the influence of silica-rich waters. It most commonly occurs in volcanic tuffs and sandstones. ## Mineral Associations This mineral often co-occurs with other secondary uranium minerals. Its most common associates include uranophane, boltwoodite, gypsum, opal (especially green-fluorescing hyalite), calcite, and less commonly other uranyl silicates. ## Localities The most important and classic haiweeite localities are in the USA, primarily at the discovery site in Inyo County, California. It is also known from other localities in Nevada and Utah. Outside the United States, good quality specimens come from La Rioja Province in Argentina (Sanogasta deposit area).

Rarity

Rare

For collectors

## Quality Criteria The collector's appeal of haiweeite depends on several factors. Specimens with well-formed, large (for this mineral) acicular crystals forming aesthetic, radial aggregates are most highly valued. The intensity and purity of the lemon-yellow color are also very important. Specimens on a contrasting rock matrix or in association with other well-formed minerals (e.g., dark opal) are particularly sought after. ## Popular Localities The best specimens in the world are considered to be those from the Sanogasta uranium deposit area in Argentina, which have yielded rich, aesthetic aggregates. Classic specimens from the type locality in California (USA) are also valued by collectors, although they are often less spectacular.

Care and storage

## Cleaning Haiweeite specimens are very delicate and brittle, so they should be cleaned with the utmost care. The safest method is to use a soft brush to remove dust or compressed air from a safe distance. Avoid washing in water, as being a hydrated mineral, it can undergo changes. Ultrasonic cleaning is prohibited. ## What to Avoid Haiweeite is a uranium mineral and is **radioactive**. Avoid direct, prolonged skin contact, and thoroughly wash hands after each contact with a specimen. Mineral dust is particularly dangerous, so situations where it could enter the respiratory or digestive tract must be avoided. The mineral is sensitive to high temperatures, which can cause dehydration and destruction. Protect it from chemicals and acids. ## Storage Due to radioactivity, haiweeite specimens should be stored in tightly sealed, labeled containers (e.g., "perky box" type), away from areas of permanent human presence, especially bedrooms. Larger or richer specimens should be kept in special shielded containers, e.g., lead-lined. Do not store it near light-sensitive materials (e.g., photographic film) or other minerals that may be sensitive to radiation (e.g., some quartz varieties).