Magnesio-dutrowite

Chemical formula: Na(Mg<sub>2.5</sub>Ti<sup>4+</sup><sub>0.5</sub>)Al<sub>6</sub>(Si<sub>6</sub>O<sub>18</sub>)(BO<sub>3</sub>)<sub>3</sub>(OH)<sub>3</sub>O

Magnesio-dutrowite is an extremely rare mineral from the tourmaline group, characterized by its black color and occurrence exclusively in the Apuan Alps, Italy.

## Characteristics Magnesio-dutrowite is a mineral belonging to the tourmaline supergroup. It forms small, columnar or acicular crystals with a black, opaque color and a submetallic luster. It typically occurs as small, radial aggregates or individual crystals embedded in the host rock, which is most often dolomitic marble. Due to its microscopic size, specimens are most often of interest to specialized collectors and scientific institutions. ## Physical Properties Its Mohs hardness is 7, which is a typical value for minerals of the tourmaline group. It has a density of approximately 3.145 g/cm³. The mineral is brittle, and its fracture is conchoidal to uneven. It has indistinct cleavage. ## Colors and Varieties Magnesio-dutrowite is an idiochromatic mineral, whose color results directly from its chemical composition. So far, only specimens of a uniform, black color have been described. No color varieties or commercial forms are known. ## History and Name The mineral was officially recognized by the International Mineralogical Association (IMA) in 2020. Its name refers to the dominant magnesium in its composition (magnesio-) and its structural relationship to dutrowite, another mineral from the tourmaline group named after American mineralogist Barbara L. Dutrow. The discovery was made by a team of researchers analyzing samples from the Apuan Alps in Italy. ## Applications Magnesio-dutrowite has no commercial or industrial applications. Its significance is purely scientific and collectible, as a unique member of the complex tourmaline family.

Properties

Mohs hardness
7
Luster
Submetallic
Streak
Gray
Density
3.145
Cleavage
Indistinct
Fracture
Conchoidal to uneven
Transparency
Opaque
Crystal system
Trigonal

Diagnostic features

## Identification Identifying magnesio-dutrowite based on visual characteristics is impossible. It occurs as a black, columnar mineral, similar to many other tourmalines. Definitive identification requires advanced analytical techniques, such as X-ray microanalysis (EDS/WDS), to determine the exact chemical composition, particularly the magnesium and titanium content. ## Distinguishing from Similar Minerals It can be confused with other black tourmalines, such as schorl, dravite, or dutrowite. It is distinguished from schorl by the dominance of magnesium over iron, and from dravite by the presence of titanium in a specific structural position. Distinguishing it from dutrowite requires precise analysis of the magnesium to titanium ratio. ## Crystal Forms It forms short, prismatic crystals, often terminated by a trigonal pyramid. Characteristic are radial aggregates composed of acicular crystals, radiating from a common center.

Geological environment

## Genesis Magnesio-dutrowite forms under conditions of regional metamorphism. Its occurrence is associated with metacarbonate rocks (calcite-dolomitic marbles) that have been subjected to high temperature and pressure. ## Mineral Associations This mineral co-occurs with calcite, dolomite, dravite, phlogopite, and pyrite. ## Localities The only confirmed locality of magnesio-dutrowite in the world is its type locality: a quarry near Fornovolasco in the municipality of Fabbriche di Vergemoli, in the Apuan Alps (Tuscany, Italy).

Rarity

Extremely rare

For collectors

## Quality Criteria As a "micromount" type mineral, specimens with well-formed, sharp crystals, forming aesthetic, radial aggregates, are most highly valued. Contrast with the light background of the host rock (marble) and the absence of damage are important. The presence of associated minerals can increase the attractiveness of the specimen. ## Popular Localities The only source of specimens is the type locality in the Apuan Alps, Italy. Material from this location is extremely limited and sought after by specialized collectors of rare minerals and research institutions.

Care and storage

## Cleaning Specimens should only be cleaned mechanically, using a soft brush to remove dust. For heavier soiling, distilled water can be used. Due to the fragility of the crystals and their often small size, utmost care must be taken. ## What to Avoid Ultrasonic cleaners should be absolutely avoided, as they can cause detachment or damage to small crystals. The use of any chemical agents, acids, or solvents is not recommended. The mineral should be protected from sudden temperature changes. ## Storage Magnesio-dutrowite specimens, most often in the form of micromounts, should be stored in sealed "micromount" boxes, which protect them from dust and mechanical damage. Direct, prolonged exposure to strong light should be avoided.

Sources

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