Petermegawite

Chemical formula: Al₆(Se⁴⁺O₃)₃[SiO₃(OH)](OH)₉(H₂O)₆·4H₂O

Petermegawite is a very rare, hydrated aluminum selenite-silicate, forming colorless, tabular crystals with a pearly luster.

## Characteristics Petermegawite is an exceptionally rare mineral from the selenite and silicate groups. It occurs as small, colorless, transparent crystals in the form of thin tablets, often grouped into rosette-like or fan-shaped aggregates. Its characteristic feature is a pearly luster on cleavage surfaces, while on other faces it is vitreous. ## Physical Properties This mineral is very soft, with a Mohs hardness of only 2-2.5, meaning it can be scratched with a fingernail. It has a density of 2.27 g/cm³, which is a relatively low value. It is transparent and brittle. ## Colors and Varieties Petermegawite is colorless. No colored varieties or trade names are known. ## History and Name The mineral was described in 2017 by Anthony R. Kampf and collaborators. Its name honors Peter K. M. Megaw, a renowned researcher and mineral collector from Mexico, for his contributions to mineralogy, particularly his research on Mexican deposits. The type locality, the first documented place of discovery, is the El Dragón mine in Bolivia. ## Applications Due to its extreme rarity and small crystal size, petermegawite has no industrial applications. It is solely an object of scientific interest and a valuable acquisition for specialized collectors of rare minerals.

Properties

Mohs hardness
2-2.5
Luster
Pearly, Vitreous
Streak
white
Density
2.27
Cleavage
{001}
Fracture
Uneven
Transparency
Transparent
Crystal system
Orthorhombic

Diagnostic features

## Identification Petermegawite can be identified by its characteristic habit of thin, colorless tabular crystals, often forming fan-shaped aggregates. Key features include a pearly luster on planes of perfect cleavage and a very low hardness (2-2.5 on the Mohs scale). ## Distinguishing from Similar Minerals It can be confused with other colorless, tabular secondary minerals, such as gypsum or some micas. It is distinguished from them by its specific habit, pearly luster, and most importantly, its environment of occurrence – oxidation zones of selenium deposits. Certain identification requires advanced analytical methods, such as Raman spectroscopy or X-ray diffraction. ## Crystal Forms Petermegawite crystals are tabular, flattened parallel to the {001} plane. They usually occur as fan-shaped or rosette-like clusters and aggregates.

Geological environment

## Genesis Petermegawite is a secondary mineral, forming in the oxidation (weathering) zones of ore deposits rich in selenium. It forms as a result of surface waters acting on primary selenium minerals in the presence of aluminum derived from the surrounding rocks. ## Mineral Associations At the type locality (El Dragón mine), petermegawite co-occurs with other rare selenites, such as chalcomenite, ahlfeldite, as well as quartz and hematite. ## Localities The only confirmed and described locality for petermegawite in the world is the El Dragón mine, located in the Potosí department of Bolivia. This is the type locality for this mineral.

Rarity

Very rare

For collectors

## Quality Criteria The most valuable petermegawite specimens are those with well-formed, transparent crystals forming aesthetic, fan-shaped or rosette-like aggregates. Due to the mineral's colorless nature, form, luster, and lack of damage are crucial. The size of crystals and aggregates also significantly increases the value of a specimen, although even microscopic samples are prized due to their rarity. ## Popular Localities The only source of collector specimens is the El Dragón mine in Bolivia, which is known for the occurrence of many unique selenite minerals.

Care and storage

## Cleaning Petermegawite specimens are extremely delicate and brittle. Cleaning should be kept to an absolute minimum. If necessary, a very soft brush can be used to remove loose dust particles. Contact with water should be avoided, as it can damage the mineral. ## What to Avoid Ultrasonic cleaners, chemicals, acids, and detergents must be absolutely avoided. The mineral is very soft, so it must be protected from scratching by harder minerals. High temperatures and direct sunlight should also be avoided. ## Storage Specimens should be stored in a separate, padded collector's box, away from other minerals, to prevent mechanical damage and abrasion. Due to its brittleness, it is not suitable for free display outside a protected container.

External references

Sources

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