Changoite

Chemical formula: Na₂Zn₂+(S₆+O₄)₂·₄H₂O

Changoite is a hydrated sodium zinc sulfate of the blödite group, forming transparent, colorless crystals.

## Characteristics Changoite is a rare mineral of the blödite group, being a hydrated sodium zinc sulfate. It occurs as small, tabular or short-prismatic crystals, which are usually colorless and transparent. It is the zinc analogue of blödite. This mineral is brittle and characterized by a vitreous luster. ## Physical Properties Changoite is a relatively soft mineral with a hardness of 2-3 on the Mohs scale. Its density is approximately 2.50 g/cm³. It exhibits a vitreous luster and is transparent. It is soluble in water. ## Colors and Varieties It is usually colorless. No colored or commercial varieties have been distinguished. ## History and Name The mineral's name comes from the pre-Columbian Chango people, who inhabited the Atacama Desert in Chile, where the mineral was discovered. Changoite was first described in 1999 by J. Schlüter, K.-H. Klask, and G. Adiwidjaja based on specimens found in the Sierra Gorda mines in the Antofagasta region of Chile. ## Uses Due to its rarity and small crystal size, changoite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals and for scientists.

Properties

Mohs hardness: 2-3
Luster: Vitreous
Streak: White
Density: 2.50
Transparency: Transparent
Crystal system: Monoclinic

Diagnostic features

## Identification Changoite is difficult to identify visually without advanced analytical methods. Its key features include occurrence in a desert climate, low hardness, water solubility, and co-occurrence with other evaporites. Positive identification requires chemical analysis (EDS/WDS) or X-ray diffraction (XRD) to confirm its composition (presence of Na, Zn, S) and crystal structure. ## Distinguishing from Similar Minerals It can be confused with other colorless, water-soluble sulfates such as blödite, mirabilite, or thenardite. It can only be distinguished from blödite (its magnesium analogue) by chemical analysis showing the presence of zinc instead of magnesium. Its crystal form and specific chemical composition distinguish it from other similar minerals. ## Crystal Forms It forms small, well-developed, tabular or short-prismatic crystals, reaching up to 2 mm in length. It occurs as single crystals or small aggregates.

Geological environment

## Genesis Changoite is a secondary mineral, formed by weathering processes in extremely dry, desert conditions (arid climate). It forms as a product of sulfide oxidation, mainly sphalerite (zinc source), in the presence of sodium-rich solutions. It is an evaporitic mineral, crystallizing from aqueous solutions in the oxidation zones of ore deposits. ## Mineral Associations This mineral co-occurs with other sulfates and salts formed under similar conditions. In its type locality (Sierra Gorda), it was found in association with blödite, lopesite-K, halite, opal, gypsum, as well as rare zinc sulfates such as gunningite and boyleite. ## Localities The most important and best-documented occurrence of changoite is its type locality - the mines in the Sierra Gorda region, Antofagasta Province, Chile. This is the only confirmed locality for this mineral worldwide.

Rarity

Very rare

For collectors

## Quality Criteria The collector's appeal of changoite is primarily determined by the quality and size of its crystals. The most valued specimens are well-formed, sharp, transparent, and freestanding crystals, even if small (around 1-2 mm). Specimens with clearly visible crystals on a rock matrix or in association with other rare minerals are rated higher than single, loose crystals. Purity (lack of inclusions) and luster also affect the specimen's value. ## Popular Localities The only source of collector specimens is the mines in the Sierra Gorda region of Chile. Specimens from this locality are the only ones available on the market and are therefore highly prized by collectors specializing in mineral systematics or minerals from specific localities.

Care and storage

## Cleaning Changoite is water-soluble, so it must absolutely not be cleaned with water. Only a soft brush or compressed air from a safe distance should be used to remove dust. ## What to Avoid Avoid all contact with water and other liquids that can dissolve the mineral. It must be protected from high humidity, which can lead to its slow degradation. High temperatures and sudden thermal changes should also be avoided. ## Storage Changoite specimens should be stored in a dry place, preferably in a sealed, airtight box (e.g., a "perky box") away from sources of moisture. It is advisable to consider using desiccants (e.g., silica gel) in the storage container.