Vimsite
Chemical formula: CaB<sub>2</sub>O<sub>2</sub>(OH)<sub>4</sub>
Wimsite is a rare hydrated calcium borate, forming colorless, acicular crystals with a silky luster.
Properties
- Mohs hardness
- 3
- Luster
- Vitreous, Silky
- Streak
- White
- Density
- 2.05
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Transparent to translucent
- Crystal system
- Monoclinic
Diagnostic features
## Identification Wimsite can be identified by its characteristic form – it creates thin, acicular crystals, often gathered in radial or woolly aggregates. It is characterized by a white color, silky luster, low hardness, and lightness. It reacts with acids, dissolving in them. ## Distinguishing from Similar Minerals Wimsite is sometimes confused with other acicular borates, such as colemanite or ulexite. It differs from colemanite by its lower hardness. Ulexite forms similar fibrous aggregates but exhibits the characteristic "television stone" effect (image conduction), which wimsite does not possess. Other similar zeolite minerals are usually harder and do not dissolve in acids as vigorously. ## Crystal Forms The mineral crystallizes in the monoclinic system, forming elongated, acicular or fibrous crystals. These crystals often arrange themselves into radial spherulites, stellar aggregates, or tangled, felt-like masses.
Geological environment
## Genesis Wimsite is a low-temperature hydrothermal mineral. It forms as a result of volcanic activity, crystallizing in cavities and fissures of volcanic rocks, such as andesites and basalts. It also forms in skarns, which are metamorphic rocks formed at the contact of magmatic intrusions with carbonate rocks (limestones, dolomites). ## Mineral Associations This mineral often co-occurs with other borates, such as kurchatovite, sibirskite, and with calcite, garnets (from the andradite group), magnetite, and pyroxenes. ## Localities The most important and classic locality for wimsite, from which the type material originates, is the Solongo boron deposit in Buryatia (Russia). Other known localities include the Fuka mine in Okayama Prefecture (Japan) and the Titovskoe boron deposit on Sakhalin (Russia).
Rarity
Very rare
For collectors
## Quality Criteria The most prized specimens by collectors are those with well-formed, radial aggregates of acicular crystals, forming aesthetic "hedgehogs" or "sunbursts" on a contrasting rock matrix. The size and completeness of these aggregates, as well as the absence of damage to the delicate needles, are important. Specimens from the classic locality (Solongo) are particularly sought after. ## Popular Localities By far the most desirable specimens come from the Solongo deposit in Russia, which has yielded the best known examples of this mineral. Specimens from the Fuka mine in Japan are also highly valued, although they typically form smaller aggregates.
Care and storage
## Cleaning Wimsite specimens are extremely delicate and brittle. They should only be cleaned very carefully, using compressed air to remove dust. Any contact with water or other liquids is inadvisable, as the mineral is partially soluble in them. ## What to Avoid Avoid contact with water, acids, and all chemical agents. The mineral is sensitive to changes in humidity and temperature. It should not be heated or exposed to direct sunlight. Any mechanical cleaning (brushes, ultrasound) is prohibited and will destroy the specimen. ## Storage Wimsite specimens should be stored in stable conditions, preferably in closed, airtight containers (e.g., "membrane box" or lidded box) that protect them from dust, moisture, and mechanical damage. Avoid places with fluctuating air humidity.