Durangite

Chemical formula: NaAlAs<sup>5+</sup>O<sub>4</sub>F

Durangite is a rare sodium aluminum arsenate, valued by collectors for its intensely orange-red, well-formed crystals.

## Characteristics Durangite is a sodium-aluminum arsenate belonging to the titanite group. This mineral typically forms small, but well-formed, prismatic or tabular crystals. Its most characteristic feature is its intense, vivid color, ranging from orange and reddish-orange to reddish-brown. Specimens often occur as single, lustrous crystals or small groups of them embedded in the host rock. ## Physical Properties Durangite crystals are characterized by a vitreous luster, and a greasy or resinous luster on fracture surfaces. It is a relatively hard mineral, which helps distinguish it from some visually similar minerals. It is transparent to translucent, and its density is noticeably higher than typical rock-forming minerals. ## Colors and Varieties The dominant and essentially only color found in durangite is orange-red in various shades. No color or commercial varieties are distinguished. ## History and Name Durangite was first described in 1869 by George J. Brush. Its name comes from its discovery locality – the Sierra de Durango mountain range in Durango State, Mexico. This is its type locality. ## Uses Durangite has no industrial application due to its rarity. However, it is a sought-after and valued collector's mineral.

Properties

Mohs hardness
5
Luster
Vitreous
Streak
Orange-yellow
Density
3.94-4.07
Cleavage
Distinct/Good on {100}
Fracture
Uneven to Conchoidal
Transparency
Transparent to Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Key diagnostic features of durangite include its monoclinic crystal habit, characteristic orange-red color, vitreous luster, and high density. Occurrence in tin-rich rhyolites is also an important clue. ## Distinguishing from Similar Minerals Durangite is sometimes confused with other orange or red minerals. It is distinguished from vanadinite by its crystal form (monoclinic, not hexagonal) and occurrence environment. It differs from cinnabar by its significantly greater hardness. Unlike some garnets, durangite has lower hardness and a different crystal habit. ## Crystal Forms Durangite crystals are typically short-prismatic, often with a nearly square cross-section, or tabular. They occur as single, overgrown crystals or in small, radial aggregates.

Geological environment

## Genesis Durangite is a pneumatolytic and hydrothermal mineral. It forms in the late stages of crystallization in alkali- and fluorine-rich rhyolites, especially those associated with tin mineralization. It crystallizes from vapors and solutions rich in arsenic, fluorine, and sodium in cavities and fractures of volcanic rocks. ## Mineral Associations This mineral often co-occurs with cassiterite, topaz, hematite, fluorite, as well as various minerals from the feldspar and mica groups. ## Localities The most important and historical locality, from which the best specimens originate, is Durango State in Mexico. It is also known from Thomas Range in Utah, USA, where it occurs in rhyolites. Other confirmed occurrences are in New Mexico (USA) and Cornwall (United Kingdom).

Rarity

Rare

For collectors

## Quality Criteria The most desirable specimens for collectors are those with sharp, well-formed, transparent crystals of intense, orange-red color. Crystals embedded on a contrasting, light rock matrix are highly valued. Crystal size is also important – specimens exceeding 1 cm are considered exceptional. ## Popular Localities By far the most prized and classic durangite specimens come from the type locality in Durango, Mexico. Specimens from Thomas Range in Utah, although usually smaller, are also sought after by collectors specializing in minerals from that locality.

Care and storage

## Cleaning Dry cleaning only is recommended, using a soft brush or compressed air to remove dust. Contact with water, especially hot water or acids, is not advisable. ## What to Avoid Avoid contact with chemicals, including acids and strong bases. The mineral is sensitive to rapid temperature changes. Prolonged exposure to direct sunlight may not be harmful, but caution is advised. ## Storage Durangite specimens are best stored in individual, padded boxes or on stands in a closed display cabinet to protect them from dust and mechanical damage. Due to its arsenic content, hands should be washed after handling the mineral.

Sources

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