Tassieite

Chemical formula: NaCa₂Mg₃Fe²⁺₂Fe³⁺(PO₄)₆·2H₂O

Tassieite is an extremely rare, greenish-brown phosphate mineral, discovered in the Mundrabilla iron meteorite in Australia.

## Characteristics Tassieite is a phosphate mineral with a complex chemical composition, belonging to the alluaudite group. It occurs as extremely small, tabular or lath-like crystals, not exceeding 50 micrometers in length, forming irregular aggregates. Its presence has only been confirmed in microscopic voids within graphite-troilite nodules in the iron meteorite. ## Physical Properties Due to the microscopic size of its crystals, most of tassieite's physical properties have not been precisely determined. The mineral is transparent to translucent, with a vitreous luster. Its hardness and density have not been measured, but the calculated density is 3.55 g/cm³. ## Colors and Varieties Tassieite crystals range in color from greenish-brown to brown. No pleochroism has been observed. No varieties of this mineral are distinguished. ## History and Name The mineral was officially recognized by the International Mineralogical Association (IMA) in 2005 (IMA2005-039). Its name honors Geoffrey Tassie (1943–1999), an Australian meteorite collector who found the specimen containing the new mineral. It was described by a team of scientists led by Gerald J. Wasserburg. ## Applications Tassieite has no practical applications. Its significance is purely scientific and as a collector's item, as a unique component of meteorites.

Properties

Color
dark green
Luster
Vitreous
Streak
light green
Density
0
Cleavage
good to perfect on {100}; a second intersects this at an angle of 60°
Transparency
Transparent
Crystal system
Orthorhombic

Diagnostic features

## Identification Identification of tassieite is possible only using advanced laboratory techniques, such as scanning electron microscopy (SEM) combined with chemical composition analysis (EDS) and X-ray diffraction (XRD). Recognition is impossible under amateur and field conditions. ## Distinguishing from Similar Minerals Tassieite is chemically and structurally related to other minerals of the alluaudite group, such as bobfergusonite, ferrowyllieite, or alluaudite. Distinguishing it from these minerals requires precise analysis of the ratio of individual cations (sodium, calcium, magnesium, iron) in the crystal structure. ## Crystal Forms The mineral forms very small, elongated, lath-like or tabular crystals that combine into irregular aggregates. These crystals typically do not exceed 50 micrometers in length and 10 micrometers in thickness.

Geological environment

## Genesis Tassieite forms under specific conditions found within some iron meteorites. Its crystallization occurs at a late stage, at low temperatures, in voids and microfractures within nodules composed of graphite and troilite. It is believed to be a product of metasomatic alteration of pre-existing phosphates, such as graftonite, in the presence of sodium- and calcium-rich fluids. ## Mineral Associations This mineral occurs in close association with other phosphates found in meteorites. It is most commonly accompanied by graftonite-(Fe), sarcopside, troilite, graphite, and other rarer phosphate minerals. ## Localities The only confirmed locality of tassieite in the world is its type locality – the Mundrabilla iron meteorite, found on the Nullarbor Plain in Western Australia.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, tassieite is not evaluated according to typical criteria such as the size or color of crystals visible to the naked eye. The value of a specimen lies in the confirmed presence of this mineral itself. The most valuable are meteorite fragments with rich, well-formed microscopic aggregates of tassieite, documented by scientific analyses. ## Popular Localities The only source of tassieite is the Mundrabilla meteorite from Western Australia. Specimens of this meteorite, even without confirmed tassieite presence, are prized by collectors of extraterrestrial material.

Care and storage

## Cleaning Specimens containing tassieite, due to their microscopic nature and embedding within the meteorite matrix, should not be subjected to any cleaning treatments. Any attempt at mechanical or chemical cleaning may irreversibly damage this extremely rare mineral. ## What to Avoid Contact with chemicals, water, and ultrasound should be avoided. The specimen should be protected from moisture, sudden temperature changes, and direct sunlight, which could affect the stability of co-occurring minerals. ## Storage Samples with tassieite should be stored under stable conditions, preferably in a specialized collector's box or display case with controlled humidity. Protection from dust and mechanical damage is crucial.

External references

Sources

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