Tarbuttite

Chemical formula: Zn²⁺₂(PO₄)(OH)

Tarbuttite is a rare, hydrated zinc phosphate, forming characteristic, lustrous crystals of varied colors, prized by collectors.

## Characteristics Tarbuttite is a hydrated zinc phosphate, occurring in the oxidation zones of zinc-bearing deposits. It forms short-prismatic, tabular, or pseudo-rhombohedral crystals, often aggregated into radial, fan-shaped, or nearly spherical clusters. Specimens are characterized by a strong, vitreous luster, which gives them a vivid, sparkling appearance. Crystals are usually small but well-formed and grown on a rock matrix, making them visually attractive. ## Physical Properties This mineral is relatively soft, with a hardness of 3.5 on the Mohs scale. Its density is approximately 4.12 g/cm³, which is a significant value for a mineral with a non-metallic appearance. Crystals are transparent to translucent and exhibit perfect cleavage in one direction. ## Colors and Varieties Tarbuttite can be colorless, white, yellow, greenish, and even reddish or brownish. The variation in colors results from the presence of impurities of other metals, mainly iron and copper. Some specimens show weak, greenish fluorescence under ultraviolet light. No named commercial or color varieties are distinguished. ## History and Name The mineral's name comes from Percy Coventry Tarbutt (1878-1943), a director of the Broken Hill Exploration Company, which managed the mine where the discovery was made. The mineral was first described in 1907 based on specimens found in the Kabwe mine in Zambia. ## Uses Tarbuttite has no industrial application and is valued solely as a collector's mineral.

Properties

Mohs hardness: 3.5
Luster: Vitreous
Streak: White
Density: 4.12
Cleavage: On {010}, perfect.
Fracture: Irregular/Uneven
Transparency: Transparent,Translucent
Crystal system: Triclinic

Diagnostic features

## Identification Characteristic features of Tarbuttite include its high vitreous luster, relatively high density, perfect cleavage, and specific crystal forms. It often occurs in association with other secondary zinc minerals, such as Hopeite, Hemimorphite, or Smithsonite. It reacts with acids. ## Distinguishing from Similar Minerals Tarbuttite is sometimes confused with Adamite, which has a similar luster and often a greenish color. However, Adamite is harder and crystallizes in the orthorhombic system, forming different crystal habits. It can also be confused with Hopeite, with which it often co-occurs, but Hopeite has a lower density and crystallizes in the orthorhombic system. ## Crystal Forms Tarbuttite crystals are typically short-prismatic, often flattened, with a pseudo-rhombohedral outline. They commonly form radial or fan-shaped aggregates, as well as granular and massive groupings.

Geological environment

## Genesis Tarbuttite is a secondary phosphate mineral, formed in the oxidation (weathering) zones of zinc deposits, especially those deposited in carbonate rocks (dolomites and limestones). It forms as a result of the reaction of phosphate-rich solutions (derived, for example, from the decomposition of organic matter or apatite) with zinc ores. ## Mineral Associations This mineral often co-occurs with other secondary zinc minerals, such as Hopeite, Parahopeite, Hemimorphite, Smithsonite, and Hydrozincite. In its type locality (Kabwe), it is also accompanied by Cerussite, Pyromorphite, and Vanadinite. ## Localities The most important and historical occurrence of Tarbuttite is the Kabwe mine (formerly Broken Hill) in Zambia, from which the world's best specimens originate. It is also known from several other localities, including the Skorpion mine in Namibia and Reaphook Hill in South Australia.

Rarity

Rare

For collectors

## Quality Criteria The most prized Tarbuttite specimens are those with well-formed, sharp, and lustrous crystals that are transparent and have an attractive color – green, yellow, and colorless specimens are particularly sought after. Rich crystal groups and aesthetic compositions on a contrasting rock matrix, most often of limonite or goethite, are also highly valued. Crystal size is crucial, and larger, undamaged specimens fetch high prices. ## Popular Localities By far the most desired specimens by collectors come from the type locality – the Kabwe mine in Zambia. They are considered the global standard for this mineral. Specimens from other locations, such as Namibia or Australia, are also interesting but rarely match the quality of those from Zambia.

Care and storage

## Cleaning Tarbuttite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. Due to its reactivity with acids, no chemical cleaning agents should be used. ## What to Avoid Tarbuttite is sensitive to acids, which can damage or destroy it. Sudden temperature changes and exposure to strong sunlight, which can cause some colored specimens to fade, should be avoided. It is a brittle mineral, susceptible to mechanical damage. ## Storage It is recommended to store specimens in separate, padded boxes or display cases to prevent scratches from harder minerals. They should be protected from dust and moisture.