Magnesiovesuvianite

Chemical formula: Ca<sub>19</sub>Mg(Al<sub>11</sub>Mg)Si<sub>18</sub>O<sub>69</sub>(OH)<sub>9</sub>

Magnesio-vesuvianite is a rare mineral from the vesuvianite group, being its magnesium analogue, forming small, prismatic crystals with a vitreous luster.

## Characteristics Magnesio-vesuvianite is a mineral belonging to the vesuvianite group, in which magnesium replaces aluminum in one of the structural sites. It forms elongated, prismatic crystals, often terminated by pyramids, reaching up to 2 mm in length. It usually occurs in the form of radial or tangled aggregates. It is brittle and characterized by a vitreous luster. ## Physical properties The hardness of magnesio-vesuvianite on the Mohs scale is approximately 6. The mineral has a vitreous luster and is transparent to translucent. Its density, calculated based on the formula and cell parameters, is 3.43 g/cm³. ## Colors and varieties Observed crystals are colorless or have a pale green tint. No named varieties of this mineral have been distinguished. ## History and name The name "magnesio-vesuvianite" refers to its chemical composition – the dominance of magnesium – and its structural relationship with vesuvianite. The mineral was approved by the International Mineralogical Association (IMA) in 2000. It was described based on material from the Jeffrey Mine in Asbestos, Quebec (Canada). ## Applications Due to its rarity and small crystal size, magnesio-vesuvianite has no industrial applications and is solely an object of interest for collectors specializing in rare minerals or minerals from the vesuvianite group.

Properties

Mohs hardness
6
Luster
Vitreous
Streak
White
Density
3.43
Cleavage
Weak on {001}, {100} and {110}
Fracture
Uneven to conchoidal
Transparency
Transparent to translucent
Crystal system
Tetragonal

Diagnostic features

## Identification Identification of magnesio-vesuvianite requires advanced research methods, such as chemical analysis (EDS/WDS) to confirm the dominance of magnesium over aluminum in a specific structural position, and X-ray diffraction (XRD) for structural analysis. Visually, it is practically indistinguishable from other colorless or pale green minerals of the vesuvianite group. ## Distinguishing from similar minerals Magnesio-vesuvianite is visually indistinguishable from vesuvianite. The difference lies in the chemical composition, where in magnesio-vesuvianite, magnesium dominates over aluminum in the Y1 site. It can also be confused with other pale green silicates found in similar environments, such as diopside or grossular, from which it is distinguished by its tetragonal crystal form. ## Crystal forms Crystals are tetragonal, prismatic in habit, elongated along the c-axis. They are usually terminated by pyramid faces. They occur as single, small crystals or in the form of radial and tangled aggregates.

Geological environment

## Genesis Magnesio-vesuvianite forms as a result of contact metamorphism processes in ultramafic rocks that have undergone metasomatism. It occurs in rodingites – rocks formed by hydrothermal alteration of mafic and ultramafic rocks, rich in calcium and poor in silica. ## Mineral associations In its type locality (Jeffrey Mine, Canada), it co-occurs with diopside, grossular, hydrogrossular, and chlorite. ## Localities The most important and best-documented occurrence of magnesio-vesuvianite is its type locality – the Jeffrey Mine in Asbestos (now Val-des-Sources), in the Estrie region, Quebec, Canada. This is the only confirmed locality of this mineral in the world.

Rarity

Very rare

For collectors

## Quality criteria The most desirable specimens are those with well-formed, transparent crystals, clearly embedded in a contrasting rock matrix. Due to the small size of the crystals (usually less than 2 mm), their quality and sharpness of form are crucial. Specimens with visible, radial aggregates are also valued. ## Popular localities All known collector specimens come from a single location in the world: the Jeffrey Mine in Quebec, Canada. This mine is now closed, meaning no new material is being extracted, and existing specimens are highly sought after.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Due to their brittleness and small crystal size, ultrasonic cleaners and strong water jets should be avoided. ## What to avoid Avoid contact with acids and other aggressive chemicals. The mineral is brittle, so it must be protected from impacts and sudden temperature changes. ## Storage It is recommended to store specimens in separate, padded boxes to prevent mechanical damage. They should be protected from dust and moisture.

Sources

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