Trolleite

Chemical formula: Al₄(PO₄)₃(OH)₃

Trolleite is a rare aluminum phosphate, prized for its pale blue or greenish massive aggregates, often found mixed with other minerals.

## Characteristics Trolleite is a rare phosphate mineral, chemically a hydrated aluminum phosphate. It most often forms massive, compact, or fibrous aggregates, rarely occurring as well-formed, small crystals. Its appearance is usually inconspicuous, and it gains collector's value through its associations with other minerals, with which it forms visually attractive rocks. ## Physical Properties This mineral is characterized by a relatively high hardness of 8.5 on the Mohs scale, which is unusual for phosphates. It has a vitreous to pearly luster, and its crystals and aggregates are typically translucent. The density of trolleite is approximately 3.1 g/cm³. ## Colors and Varieties Typical colors of trolleite include light blue, blue-green, green, or yellowish-green. It does not have named varieties, but in trade, rocks (usually quartzitic) containing this mineral as blue inclusions, often accompanied by lazulite, scorzalite, or augelite, are frequently referred to as "trolleite." These mineral mixtures, mainly from Brazil, are polished and sold as ornamental stones. ## History and Name The mineral's name comes from Hans Gabriel Trolle-Wachtmeister (1782-1871), a Swedish chemist and Attorney General, who first described it. Trolleite was discovered and described in 1868 based on samples collected from the iron mine in Västanå (Scania, Sweden). ## Uses Due to its rarity, trolleite has no industrial applications. It is a valued collector's mineral, and its mixtures with quartz and other blue phosphates are used as gemological material for making cabochons, beads, and small carvings.

Properties

Mohs hardness: 8.5
Luster: Vitreous, Pearly
Streak: White
Density: 3.09–3.12
Cleavage: Good on {100}
Fracture: Uneven
Transparency: Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Massive trolleite is primarily identified by its characteristic pale blue or greenish color, vitreous luster, and high hardness (8.5), which is a key feature distinguishing it from most other phosphates. Its occurrence in association with other phosphates, such as lazulite or scorzalite, is also a strong indicator. ## Distinguishing from Similar Minerals Trolleite is sometimes confused with lazulite, which, however, has a more intense, dark blue color and is significantly softer (hardness 5.5-6). It is distinguished from quartz by its higher hardness and density. In massive form, it may resemble serpentine or some beryl varieties, but a hardness test is conclusive in this case. ## Crystal Forms Well-formed trolleite crystals are extremely rare and small, usually prismatic or tabular. It is most commonly found in compact, massive, or radially fibrous aggregates, often as inclusions in quartz.

Geological environment

## Genesis Trolleite is a metamorphic mineral. It forms in aluminum- and phosphorus-rich rocks that have undergone high-pressure and high-temperature metamorphism. It typically occurs in quartzites, as well as in pegmatites and hydrothermal veins cutting through metamorphic rocks. ## Mineral Associations This mineral often co-occurs with other phosphates, such as lazulite, scorzalite, augelite, wagnerite, as well as andalusite, kyanite, sillimanite, goyazite, topaz, and quartz. ## Localities The most important trolleite localities worldwide include: - Sweden: Västanå mine in the Scania region (type locality). - Brazil: Minas Gerais state, from where most of the ornamental material sold as "trolleite" originates. - Australia: near Gumeracha in South Australia. - Rwanda: Burera District. - USA: White Mountains in California.

Rarity

Rare

For collectors

## Quality Criteria The most prized trolleite specimens are those that form well-developed, even if small, crystals. For massive material, the intensity and uniformity of the blue or greenish color and the aesthetic distribution within the host rock (usually white quartz) determine its value. The color contrast between pale blue trolleite and, for example, dark blue lazulite in the same sample is highly desirable. ## Popular Localities For systematic mineral collectors, specimens from the type locality in Sweden are most valuable. However, in the market for ornamental stones and polished specimens, material from Minas Gerais, Brazil, absolutely dominates, offering the most visually attractive color combinations.

Care and storage

## Cleaning Trolleite specimens should only be cleaned with lukewarm distilled water and a soft brush. Ultrasonic cleaners should be avoided, as they can damage mineral aggregates, especially if they occur in brittle quartz. ## What to Avoid The mineral is sensitive to strong acids and bases. Sudden temperature changes and prolonged exposure to direct sunlight should be avoided, as theoretically, this can cause some specimens to fade. ## Storage Specimens should be stored in stable conditions, away from dust and chemicals. Due to its hardness, it can scratch other minerals, so it is best to store it in separate boxes or on a soft surface.

Sources

IMA Mineral List (CNMNC)