Bultfonteinite

Chemical formula: Ca<sub>2</sub>[SiO<sub>3</sub>(OH)]F·H<sub>2</sub>O

A rare pink calcium silicate, forming radial aggregates of tiny, acicular crystals.

## Characteristics Bultfonteinite is a hydrated calcium silicate with additional fluorine ions and hydroxyl groups. It most commonly occurs as spherical or radial aggregates, which consist of very fine, acicular or fibrous crystals. Individual, well-formed crystals are extremely rare and reach only a few millimeters in length. This mineral is prized for its delicate pink color and characteristic radial structure of its aggregates. ## Physical Properties Bultfonteinite crystals exhibit a hardness of 4.5 on the Mohs scale. They have a vitreous luster and are transparent to translucent. The mineral's density is approximately 2.73 g/cm³. It is relatively brittle. ## Colors and Varieties Bultfonteinite is most often colorless, white, or pale pink. The pink coloration is the most typical and sought after by collectors. No named varieties are distinguished. ## History and Name The mineral was discovered in the Bultfontein mine in Kimberley, Republic of South Africa. Its name, given in 1932 by John Parry, comes directly from its discovery locality. This mine, along with neighboring diamond mines, is the type locality for this mineral. ## Uses Bultfonteinite has no industrial application. It is solely a mineral of scientific and collector interest.

Properties

Mohs hardness
4.5
Luster
Vitreous
Streak
White
Density
2.73
Cleavage
Perfect on {100}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Triclinic

Diagnostic features

## Identification A characteristic feature of bultfonteinite is its radial, spherical aggregates composed of tiny, acicular crystals. The pinkish coloration in combination with this form of occurrence is a strong diagnostic indicator. It occurs in a specific geological environment, which also aids in identification. ## Distinguishing from Similar Minerals Bultfonteinite is sometimes confused with other minerals forming radial aggregates, such as natrolite or scolecite. It is distinguished from them by its lower hardness (4.5 compared to 5-5.5 for zeolites) and different environment of occurrence (contact-metasomatic rocks, not gas bubbles in basalts). Final confirmation requires advanced studies, e.g., by XRD method. ## Crystal Forms Crystals are elongated, acicular, or fibrous. They almost always occur as radial, spherulitic aggregates. Single, isolated crystals are rarely observed.

Geological environment

## Genesis Bultfonteinite forms as a result of hydrothermal and metasomatic processes at the contact of diabase intrusions with limestones or in kimberlite breccias. It forms in veins and fissures cutting calcium-rich rocks. ## Mineral Associations This mineral often co-occurs with calcite, apophyllite, okenite, and also with minerals from the zeolite group. In its type locality, it was found in association with afwillite and scawtite. ## Localities The most important and well-known localities of bultfonteinite are in the Republic of South Africa, in the Kimberley diamond mine complex (Bultfontein, Dutoitspan, Wesselton mines). It is also known from the N'Chwaning mine in Kuruman (Kalahari Desert). Outside South Africa, its occurrences have been reported in the USA (Crestmore, California) and in Israel (Hatrurim Formation).

Rarity

Rare

For collectors

## Quality Criteria The most highly prized bultfonteinite specimens are those that form well-defined, spherical aggregates with an intense pink coloration. The absence of damage to the delicate needles and aesthetic placement on the rock matrix, often accompanied by contrasting minerals like white calcite, are important. The size of the aggregates also affects value, with specimens several centimeters in diameter already considered significant. ## Popular Localities Specimens from the mines in the Kuruman region of the Kalahari Desert in South Africa (e.g., N'Chwaning mines) are by far the most sought after by collectors. They are characterized by the best development and most intense color.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Brief rinsing in distilled water is permissible, followed by thorough drying. Ultrasonic cleaners should be avoided, as they can damage delicate aggregates. ## What to Avoid The mineral is sensitive to acids. Contact with household and laboratory chemicals should be avoided. It should not be heated, as it contains water in its crystal structure and may dehydrate. ## Storage Bultfonteinite aggregates are very brittle and susceptible to mechanical damage. It is best to store them in closed collector boxes, lined with soft material, away from specimens of greater hardness. They should be protected from dust and shocks.

External references

Sources

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