Dutrowite

Chemical formula: Na(Fe²⁺₂.₅Ti⁴⁺₀.₅)Al₆(Si₆O₁₈)(BO₃)₃(OH)₃O

Dutrowite is a rare, black mineral from the tourmaline group, distinguished by its high titanium and iron content, discovered in Italy.

## Characteristics Dutrowite is a mineral belonging to the tourmaline supergroup. It forms black, opaque crystals with a prismatic or acicular habit, often terminated pyramidally. It typically occurs as well-formed crystals embedded in rock, reaching up to several millimeters in length. Its characteristic features are its black, opaque color and vitreous luster. ## Physical Properties This mineral is characterized by significant hardness, measuring 7 on the Mohs scale, which is typical for tourmalines. It has a vitreous luster and is brittle, with an uneven, conchoidal fracture. The density of dutrowite is relatively high, approximately 3.25 g/cm³. ## Colors and Varieties Dutrowite is an idiochromatic mineral, whose intensely black color results from its chemical composition, specifically the presence of iron and titanium. No color varieties or commercial varieties are distinguished. ## History and Name The mineral is named in honor of Barbara L. Dutrow, an American mineralogist and professor at Louisiana State University, for her contributions to research on the tourmaline group. Dutrowite was approved as a new mineral by the International Mineralogical Association (IMA) in 2017. It was discovered in the Grotta del Vento area, Fornovolasco, in the Apuan Alps, Italy. ## Applications Due to its rarity and small crystal size, dutrowite has no industrial applications. It is solely an object of scientific and collecting interest for advanced collectors of systematic minerals and micromounts.

Properties

Mohs hardness
7-7.5
Color
brown
Luster
Vitreous
Streak
light brown
Density
3.203
Cleavage
None
Fracture
Irregular/Uneven
Transparency
Transparent
Crystal system
Trigonal

Diagnostic features

## Identification Macroscopic identification of dutrowite is difficult and requires advanced research methods. It is identified based on its black color, trigonal crystal form, high hardness (7 on the Mohs scale), and characteristic occurrence environment. Definitive identification is only possible using chemical analysis (EDS) and X-ray diffraction methods (XRD). ## Distinguishing from Similar Minerals Dutrowite is almost impossible to distinguish with the naked eye from other black tourmalines, such as schörl, dravite, or iron-rich elbaite. The differences arise from the chemical composition, particularly the high titanium content unique to dutrowite. Distinguishing it from these minerals requires specialized research equipment. ## Crystal Forms Dutrowite forms prismatic or acicular crystals with a triangular cross-section and rounded faces, which is typical for tourmalines. Crystals are often terminated by low-angle trigonal pyramid faces. They occur as single, embedded crystals or in small, radial aggregates.

Geological environment

## Genesis Dutrowite forms under conditions of regional metamorphism, in rocks rich in aluminum and boron. Its formation is associated with hydrothermal processes occurring at moderate temperatures and pressures. In its type locality (Apuan Alps), it occurs in veins cutting metagranite lenses within schists. ## Mineral Associations This mineral co-occurs with quartz, muscovite, hematite, phlogopite, clinochlore, titanite, and other tourmalines such as dravite and schörl. ## Localities The only confirmed and thoroughly described locality of dutrowite worldwide is its discovery site: the Grotta del Vento area, Fornovolasco, Province of Lucca, Tuscany, Italy.

Rarity

Very rare

For collectors

## Quality Criteria The quality of dutrowite specimens is primarily assessed based on crystal development and size. The most valued are well-formed, sharply terminated crystals that stand out clearly against the light background of the host rock (most often quartz or muscovite). Luster and absence of mechanical damage also increase collector value. ## Popular Localities All known collector specimens come from a single locality – Fornovolasco, Italy. Material from this location is extremely limited, making it highly sought after by collectors specializing in tourmalines and systematic minerals.

Care and storage

## Cleaning Dutrowite specimens should only be cleaned mechanically, using a soft, dry brush to remove dust. Due to its occurrence as embedded, small crystals, wet cleaning is not recommended as it could damage the host rock. ## What to Avoid Avoid contact with strong chemical agents, acids, and bases. Despite its high hardness, the mineral is brittle and sensitive to impacts and sudden temperature changes. It should not be subjected to ultrasonic cleaning. ## Storage Collector specimens of dutrowite, especially micromounts, are best stored in specialized closed boxes (such as "membrane boxes" or padded boxes) that protect them from dust, moisture, and mechanical damage.

External references

Sources

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