Tomiolloite

Chemical formula: Al<sub>12</sub>(Te<sup>4+</sup>O<sub>3</sub>)<sub>5</sub>[(S<sup>4+</sup>O<sub>3</sub>)<sub>0.5</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>0.5</sub>](OH)<sub>24</sub>

Tomiolloite is an extremely rare aluminum tellurite, forming microscopic, colorless crystals in volcanic exhalation products.

## Characteristics Tomiolloite is a mineral from the tellurite group, chemically a complex aluminum tellurite-sulfite-sulfate. It occurs as extremely small, tabular or bladed crystals, usually not exceeding 50 micrometers in length and a few micrometers in thickness. The crystals are colorless and transparent, often forming disordered aggregates or fan-shaped clusters on the surface of altered volcanic rocks. ## Physical Properties Due to the microscopic size of the crystals, most physical properties have not been precisely determined. Hardness is too low to scratch glass. Luster is described as vitreous to pearly, especially visible on crystal faces. The mineral is transparent. ## History and Name The mineral was approved by the International Mineralogical Association (IMA) in 2012 under number 2012-068. Its name honors Franco Tomiollo, an Italian micro-mineral collector who found the first samples. It was discovered in fumarole products on Mount Vesuvius in Italy. ## Uses Tomiolloite has no industrial application. It is solely an object of scientific interest and a valuable acquisition for specialized collectors of microscopic minerals.

Properties

Mohs hardness
2
Luster
Vitreous to Pearly
Streak
White
Density
2.55
Cleavage
Perfect on {0001}
Fracture
Micaceous
Transparency
Transparent
Crystal system
Trigonal

Diagnostic features

## Identification Identification of tomiolloite is only possible using advanced analytical methods, such as Raman spectroscopy and X-ray microanalysis (EDS/WDS) in conjunction with X-ray diffraction (XRD). Visually, in the field or in a collection, it is indistinguishable from many other microscopic secondary minerals. ## Distinguishing from Similar Minerals Under the microscope, it may resemble other colorless, microscopic sulfates, sulfites, or tellurites found in the same environment, such as alunogen, gypsum, or other rare fumarolic minerals. Definitive differentiation requires specialized laboratory equipment. ## Crystal Forms It forms very small, thin, tabular crystals with a hexagonal outline, elongated in one direction. Crystals often combine into fan-shaped or irregular aggregates.

Geological environment

## Genesis Tomiolloite is a fumarolic mineral. It forms as a result of direct sublimation from volcanic gases or in reaction of these gases with alteration products of volcanic rocks in a low-temperature environment (below 100°C). ## Mineral Associations It co-occurs with other exhalative minerals such as alunogen, mascagnite, sassolite, native sulfur, and newly discovered, rare tellurites and sulfates. ## Localities The only confirmed occurrence of tomiolloite in the world is its type locality - fumaroles in the La Fossa crater on Vulcano Island, part of the Aeolian Islands archipelago in Italy.

Rarity

Extremely rare

For collectors

## Quality Criteria For micromineral collectors, the size and quality of the crystals are most important - the larger, better-formed, and more transparent they are, the more valuable the specimen. Rich clusters of crystals on a small rock matrix surface and associations with other rare minerals are also highly prized. ## Popular Localities The only source of tomiolloite specimens is its discovery site: Vulcano volcano in Italy. All specimens available on the collector's market come from this single location.

Care and storage

## Cleaning Tomiolloite specimens should generally not be cleaned. The crystals are extremely small and fragile, and any attempt at mechanical cleaning (brush, compressed air) or chemical cleaning risks their irreversible destruction. ## What to Avoid Contact with water and all chemicals should be strictly avoided. The mineral is likely soluble in acids. It should be protected from vibrations, shocks, and sudden temperature changes. It should not be heated. ## Storage Microscopic tomiolloite specimens should be stored exclusively in tightly sealed "micromount" boxes to protect them from dust, moisture, and mechanical damage. Display is only possible under a microscope.

Sources

Read more