Maxwellite

Chemical formula: NaFe³⁺As⁵⁺O₄F

Maxwellite is a rare sodium-iron arsenate, forming small, vitreous crystals ranging in color from yellow to reddish-brown.

## Characteristics Maxwellite is a sodium-iron arsenate belonging to the tilasite group. It occurs as very small, tabular or prismatic crystals, rarely exceeding 1 mm in length. It typically forms radial aggregates or rosettes. It is a transparent to translucent mineral with a vitreous luster. ## Physical Properties The mineral is characterized by a hardness of approximately 5 on the Mohs scale. Its density is quite high, around 4.13 g/cm³. The crystals exhibit good cleavage in one direction. ## Colors and Varieties Maxwellite most commonly ranges in color from light yellow, through yellowish-green, to reddish-brown. Some crystals may exhibit pleochroism, a change in hue depending on the observation direction, ranging from colorless to pale yellow. No varieties have been distinguished. ## History and Name The mineral was named in honor of Charles Henry Maxwell (1920-2012), an American geologist who worked for the U.S. Geological Survey, in recognition of his contributions to the study of geology and ore deposits in New Mexico. It was approved as a new mineral by the IMA in 1988, and its description was published in 1992. The type locality is Squaw Creek in New Mexico, USA. ## Uses Maxwellite has no industrial applications. Due to its rarity and small crystal size, it is solely an object of interest for collectors specializing in rare minerals or minerals from specific localities.

Properties

Mohs hardness
5-5.5
Color
Red
Luster
Vitreous
Streak
Pale red-orange to red-orange
Density
3.90
Cleavage
{110}
Fracture
Irregular/Uneven
Transparency
Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Maxwellite is identified by its characteristic appearance – small, tabular crystals forming radial aggregates. Its yellow to reddish-brown color, vitreous luster, and high density are also helpful. However, definitive identification requires advanced analytical methods such as chemical analysis (EDS) or X-ray diffraction (XRD), due to its similarity to other arsenates. ## Distinguishing from Similar Minerals It can be confused with other minerals from the tilasite group, such as tilasite or arseniopleite, with which it forms solid solution series. Distinguishing it from these is almost exclusively possible through chemical analysis. Visually, it may resemble some microcrystalline micas or other secondary arsenic minerals. ## Crystal Forms Crystals are usually very small, with a tabular or short-prismatic habit. They most often occur as radial or stellate aggregates, as well as scattered, individual crystals on the surface of the host rock.

Geological environment

## Genesis Maxwellite is a secondary mineral, forming in the oxidation zones (gossans) of ore deposits. It forms in an arsenic-rich environment as a result of the weathering of primary arsenic minerals. It occurs in fractures and voids in volcanic rocks, such as rhyolites. ## Mineral Associations This mineral co-occurs with other arsenates and secondary minerals. At the type locality (Squaw Creek), it was found in association with quartz, hematite, adularia, beudantite, segnitite, agardite-(Y), mimetite, and pharmacosiderite. ## Localities The most important and best-documented occurrence of maxwellite is its type locality – Squaw Creek, Catron County, New Mexico, USA. Additionally, its presence has been reported in the Clara Mine in the Black Forest (Germany) and in a polymetallic deposit in the Attica region of Greece. These are the only confirmed localities worldwide.

Rarity

Very rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with well-formed, sharp crystals forming aesthetic, radial aggregates. The contrasting, bright color of the crystals on a darker host rock (matrix) significantly enhances the specimen's appeal. Due to their small size, microscopic quality is crucial – the clarity and lack of damage to individual crystals within the aggregate. ## Popular Localities By far, the most sought-after specimens come from the type locality in New Mexico, USA, which has yielded the best-known examples of this mineral.

Care and storage

## Cleaning Maxwellite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to the presence of arsenic, avoid inhaling dust and wash hands after handling the mineral. Wet cleaning is not recommended. ## What to Avoid Avoid contact with chemicals, especially acids, which can damage the mineral. It should not be heated or subjected to ultrasound. Store away from moisture. ## Storage It is recommended to store specimens in sealed, dry containers or display boxes to protect them from dust and mechanical damage. Due to the small size of the crystals, boxes with magnification (so-called micromounts) are ideal.

External references

Sources

Read more