Amarillite

Chemical formula: NaFe<sup>3+</sup>(S<sup>6+</sup>O<sub>4</sub>)<sub>2</sub>·6H<sub>2</sub>O

Amarillite is a rare, water-soluble sodium-iron sulfate, forming bright yellow, granular aggregates in arid climates.

## Characteristics Amarillite is a hydrated sodium and iron sulfate, occurring as fine-grained or earthy aggregates. It rarely forms small, tabular or prismatic crystals, which usually do not exceed a few millimeters. Its name refers to its characteristic bright yellow color (Spanish: *amarillo* - yellow). ## Physical Properties This mineral is very soft and brittle. It has a vitreous luster and is transparent to translucent. Due to its water solubility, it is unstable in humid environments and requires special storage conditions. ## Colors and Varieties Amarillite occurs in shades from pale yellow to canary yellow. No color or commercial varieties are distinguished. ## History and Name The mineral's name, given in 1914 by Arturo Posnjak, comes from the Spanish word *amarillo* meaning "yellow," which is a direct reference to its typical color. It was discovered in the Tierra Amarilla mines in the Atacama region of Chile. ## Uses Amarillite has no industrial application. It is solely an object of interest for collectors specializing in rare minerals or minerals from specific localities.

Properties

Mohs hardness
2.5
Luster
Vitreous
Streak
Pale yellow
Density
2.19
Cleavage
Perfect on {010}
Fracture
Conchoidal
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification A key diagnostic feature of amarillite is its reaction to water – the mineral rapidly dissolves in it. Its bright yellow color, low hardness, and occurrence as granular coatings and aggregates in dry, desert environments are also characteristic. ## Distinguishing from Similar Minerals Amarillite can be confused with other secondary iron sulfates, such as coquimbite, copiapite, or metavoltine. Distinguishing them without advanced methods (like X-ray diffraction) is very difficult. Co-occurrence with other specific minerals, such as leonite or blödite, and a precise analysis of crystal form, if present, can be key. ## Crystal Forms Amarillite crystallizes in the monoclinic system. Its crystals are rare and usually appear as small, tabular or short prisms. It is most commonly found as granular, powdery aggregates or as a component of efflorescences on other minerals.

Geological environment

## Genesis Amarillite is a secondary mineral, formed by the oxidation of sulfide deposits (mainly pyrite) in extremely dry, desert conditions. It forms as an evaporation product of waters rich in sodium and iron sulfates on the Earth's surface or in shallow subsurface zones. ## Mineral Associations It most commonly co-occurs with other sulfates and evaporite minerals, such as leonite, blödite, coquimbite, copiapite, chalcanthite, gypsum, and native sulfur. ## Localities The most important and classic amarillite localities are in the Atacama Desert in Chile, particularly in the Tierra Amarilla region (from which the name originates), Chuquicamata, and the Alcaparrosa mine. It also occurs in other arid regions of the world, for example, in Argentina.

Rarity

Rare

For collectors

## Quality Criteria For collectors, specimens with well-formed, even if small, crystals are most desirable, which is a great rarity for this mineral. Rich, intensely yellow aggregates on a contrasting rock matrix are also valued. Association with other rare sulfates is also important. ## Popular Localities The most classic and valued specimens by collectors come from historical localities in Chile, such as Tierra Amarilla and Chuquicamata. Material from these places is considered exemplary for this species.

Care and storage

## Cleaning This mineral must absolutely not be cleaned wet, as it is water-soluble. Dust can only be removed using a soft, dry brush or very carefully, using a stream of compressed air from a safe distance. ## What to Avoid Avoid all contact with water, water vapor, and high humidity, which can cause the specimen to dissolve and disintegrate. It should also be protected from contact with chemicals. It is a very delicate and brittle mineral, sensitive to impact and scratches. ## Storage Amarillite specimens must be stored in sealed, dry containers, preferably with a desiccant (e.g., silica gel). The best solution is sealed "membrane box" type containers or airtight display cases. Display should be in a room with controlled, low humidity.

Sources

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