Thadeuite

Chemical formula: CaMg₃(PO₄)₂(OH,F)₂

Thadeuite is a rare calcium and magnesium phosphate, forming colorless or white, acicular crystals with a silky luster.

## Characteristics Thadeuite is a rare mineral from the phosphate group, chemically classified as a hydrated calcium and magnesium phosphate with fluorine. It occurs as aggregates of small, acicular or fibrous crystals, which can form radial aggregates or mats. Individual crystals are usually very small, rarely exceeding a few millimeters in length. The mineral is colorless to white and is characterized by a silky luster, resulting from its fibrous structure. ## Physical Properties Thadeuite has a hardness of about 4 on the Mohs scale. Its crystals are flexible, which is an unusual characteristic for phosphates. The mineral's density is approximately 2.93 g/cm³. The luster is silky, and the mineral is translucent. ## Colors and Varieties This mineral is usually colorless or white. No color or commercial varieties have been distinguished. ## History and Name Thadeuite was discovered in a granitic pegmatite in the Anjahamiary mine, near Malakialina, Madagascar. It was described and approved as a new mineral species in 1979. Its name honors Thadeus ("Thad") L. B. Goss (1915-1978), an American mineralogist and collector, who first noticed this mineral and submitted it for study. ## Uses Due to its extreme rarity and small crystal size, thadeuite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals and for scientists.

Properties

Mohs hardness
3.5-4
Color
yellow-orange, brown
Luster
Silky
Streak
white
Density
3.24
Cleavage
{010}
Fracture
Splintery
Transparency
Transparent
Crystal system
Orthorhombic

Diagnostic features

## Identification Thadeuite can be recognized by its characteristic mode of occurrence – it forms white or colorless, silky aggregates of small, acicular crystals. Its flexibility is also a diagnostic feature, although difficult to verify without damaging the sample. Its occurrence in a specific pegmatitic environment in association with other phosphates is a key indicator. ## Distinguishing from Similar Minerals Thadeuite can be confused with other fibrous secondary minerals, such as some zeolites (e.g., natrolite) or other rare phosphates. However, natrolite is harder (5-5.5) and has a different genesis. Precise identification requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS). ## Crystal Forms Thadeuite crystals are strongly elongated, acicular or hair-like, with a bladed cross-section. They usually occur as tangled aggregates, radial aggregates, or mats covering other minerals.

Geological environment

## Genesis Thadeuite is a hydrothermal mineral, crystallizing in the late stages of granitic pegmatite evolution. It forms in rock cavities and fissures as a result of the activity of solutions rich in phosphorus, magnesium, and fluorine. ## Mineral Associations This mineral co-occurs with other phosphates and pegmatitic minerals. At its type locality (Anjahamiary, Madagascar), it was found in association with lazulite, augelite, wardite, trolleite, apatite, quartz, albite, and muscovite. ## Localities The only confirmed and well-documented locality for thadeuite in the world is its discovery site – the pegmatite in the Anjahamiary mine, in the Betafo district, Vakinankaratra region, Madagascar.

Rarity

Extremely rare

For collectors

## Quality Criteria The most prized thadeuite specimens are those that possess rich, dense aggregates of well-formed, silky needles, contrasting with the rock matrix. The presence of associated minerals, confirming the paragenesis from the type locality, is also important. Due to the microscopic size of the crystals, the overall size of the specimen and the aesthetic composition play a key role in its evaluation. ## Popular Localities The only source of collector specimens is the Anjahamiary mine in Madagascar. Material from this location is extremely difficult to acquire on the market.

Care and storage

## Cleaning Thadeuite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its fibrous and delicate nature, washing in water should be avoided, as it could damage the fragile aggregates. If liquid is necessary, isopropyl alcohol applied in a small amount is recommended. ## What to Avoid Contact with acids and other chemicals that may react with phosphates should be avoided. The mineral is relatively soft, so it must be protected from scratching by harder minerals. Avoid ultrasonic cleaning machines, which would destroy delicate crystal aggregates. ## Storage Thadeuite specimens are best stored in sealed collector boxes, lined with soft material, to protect them from dust, moisture, and mechanical damage. It should be kept away from minerals that could scratch it.

External references

Sources

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