Benstonite
Chemical formula: Ba<sub>6</sub>Ca<sub>6</sub>Mg(CO<sub>3</sub>)<sub>13</sub>
A rare barium, calcium, and magnesium carbonate, forming characteristic white or cream-colored aggregates with a granular or felted texture.
Properties
- Mohs hardness
- 3-4
- Luster
- Vitreous
- Streak
- White
- Density
- 3.596-3.69
- Cleavage
- Perfect on {1011}
- Fracture
- Uneven
- Transparency
- Translucent
- Crystal system
- Trigonal
Diagnostic features
## Identification The most important diagnostic feature of benstonite is its strong, red or orange-red fluorescence under shortwave UV light (SW-UV) and the often accompanying phosphorescence (glowing after the UV source is turned off). It reacts violently with hydrochloric acid, effervescing. Its relatively high density for a carbonate is also a helpful indicator. ## Distinguishing from Similar Minerals It can be confused with other white, massive carbonates such as calcite, dolomite, or barytocalcite. It is distinguished from calcite and dolomite by its significantly higher density. From barytocalcite, with which it often co-occurs, it can be distinguished by crystal habit (if present) and the characteristic red fluorescence in SW-UV, which barytocalcite typically does not exhibit. ## Crystal Forms Well-formed crystals are rare. They usually appear as thick, rhombohedral or pseudo-hexagonal tablets. Most commonly, it is found in compact, granular, or felted masses, as well as vein fillings and cement in breccias.
Geological environment
## Genesis Benstonite is a hydrothermal mineral. It forms at low to medium temperatures in carbonate veins, often associated with barite, manganese, or rare earth element deposits. It forms in environments rich in barium, calcium, and carbon dioxide. ## Mineral Associations This mineral often co-occurs with other carbonates and sulfates. Its most common associated minerals include: barite, calcite, barytocalcite, fluorite, quartz, alstonite, as well as rarer minerals like norsethite or witherite. ## Localities The most important and classic locality, from which the best specimens originate, is Magnet Cove in Hot Spring County, Arkansas (USA). Other known localities include the manganese ore deposit in Långban, Sweden; the Rosh Pinah mine in Namibia; and occurrences in Canada (near Lake Superior), India (Joda mine), and China.
Rarity
Rare
For collectors
## Quality Criteria The most prized specimens by collectors are those with well-formed, sharp crystals, which is a great rarity for this mineral. Rich aggregates with intense, red fluorescence are also highly valued. Contrasting associations with other minerals, e.g., dark fluorite, enhance the attractiveness of the specimen. Size and purity (lack of damage) are also key factors influencing value. ## Popular Localities By far the most sought-after specimens come from the type locality – Magnet Cove in Arkansas, USA. These are considered the global standard for this mineral. Specimens from Långban, Sweden, are also valued, although they often have a different form and character.
Care and storage
## Cleaning Benstonite is sensitive to acids, which cause it to effervesce violently and decompose. For cleaning, use only distilled water and a very soft brush or cloth. Ultrasonic cleaners should be avoided. ## What to Avoid Contact with acids (even weak ones, like vinegar or lemon juice) must be strictly avoided. The mineral is brittle and sensitive to impacts and scratches. It should not be heated or exposed to sudden temperature changes. ## Storage Benstonite specimens are best stored in separate, padded boxes to prevent scratches and chipping. Due to its brittleness, it should not be stored loosely with harder minerals. It is stable under household conditions and does not require special humidity control or protection from light.