Blodite-series

Chemical formula: Na₂(Mg,Mn,Ni)[SO₄]₂[H₂O]₄

The blödite series is a group of hydrated sodium, magnesium, manganese, and nickel sulfates, forming crystals or efflorescences in drying salt lakes and evaporite deposits.

## Characteristics The blödite series comprises several related hydrated sulfate minerals. Individual minerals in the series differ in their dominant element: magnesium (blödite), manganese (changoite), or nickel (nickelblödite). The most commonly encountered member of the group is blödite. It typically forms short, prismatic or tabular crystals, often with a rich number of faces. It also occurs as granular aggregates, compact masses, and as efflorescences and crusts on other minerals or rocks. ## Physical Properties Minerals from this series are characterized by low hardness, ranging from 2.5-3 on the Mohs scale, meaning they can be scratched with a copper wire. They have a vitreous luster and are transparent to translucent. The density of blödite is approximately 2.23 g/cm³, making it a relatively light mineral. A characteristic feature is its solubility in water. ## Colors and Varieties The color of minerals in the series depends on their chemical composition. Pure blödite (magnesium-rich) is colorless, white, grayish, or pale yellow. Changoite, containing manganese, takes on yellowish-green hues. Nickelblödite, as the name suggests, is green due to its nickel content. The varieties are the individual minerals (members) of the series. ## History and Name The name of the most popular mineral in the series, blödite, was given in 1828 by John George Children. He honored the German chemist and mineralogist Karl August Blöde (1773-1820). The mineral was first described based on specimens from a salt mine near Ischl in Austria. ## Applications Minerals from the blödite series do not have significant industrial applications. They are primarily of interest to collectors and scientists studying the formation processes of salt deposits (evaporites).

Properties

Mohs hardness: 2.5-3
Luster: Vitreous
Streak: White
Density: 2.23
Cleavage: Perfect on {010}, good on {10-1}
Fracture: Conchoidal
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Key diagnostic features of minerals from this series are: occurrence environment (evaporite deposits), low hardness, vitreous luster, and characteristic short prismatic crystals. The most important diagnostic test is complete solubility in water. The mineral also has a salty-bitter taste, but taste testing is not a recommended or safe identification method. ## Distinguishing from Similar Minerals Blödite is sometimes confused with other evaporite sulfates. It differs from gypsum by its greater hardness and solubility in water. It differs from thenardite by its crystal habit (thenardite crystallizes in the orthorhombic system) and the presence of water in its structure. Mirabilite is much less stable and quickly effloresces (loses water) in dry air. Halite (rock salt) has perfect, three-directional cleavage and crystallizes in the isometric system, forming cubic crystals. ## Crystal Forms Crystals are typically short-prismatic, tabular, or nearly isometric, often with complex morphology and a large number of faces. It occurs as single, overgrown crystals, as well as in granular, compact aggregates, and as crusts or efflorescences.

Geological environment

## Genesis Minerals from the blödite series are typical products of the evaporation of waters rich in sulfates and sodium chloride. They form in arid and hot climates, crystallizing directly from brines in drying lakes, lagoons, salt marshes (playas), and marine sedimentary basins. They can also form as secondary efflorescences on the surface of soils and rocks in desert areas. ## Mineral Associations They most often co-occur with other salt minerals, such as halite, thenardite, mirabilite, glauberite, epsomite, polyhalite, and gypsum. The composition of the associated mineral assemblage depends on the chemistry of the primary brine and the crystallization conditions. ## Localities Significant deposits and well-formed blödite crystals come from many places around the world. Classic localities include salt mines in Austria (Hallstatt, Bad Ischl). In the USA, beautiful specimens have been found in Soda Lake and Searles Lake in California, and in the Great Salt Lake in Utah. The Atacama Desert in Chile is an important source of blödite, as well as a type locality for the rarer members of the series – changoite (Salar de Pintados) and nickelblödite.

Rarity

Not very common

For collectors

## Quality Criteria The most valued by collectors are well-formed, fully transparent crystals with sharp edges and smooth faces. Large size is a significant asset. Specimens of intensely colored varieties, such as green nickelblödite, are particularly sought after. Aesthetic compositions of blödite with other contrasting evaporite minerals, such as pink halite, are also highly regarded. ## Popular Localities Specimens from classic localities in Austria and from American salt lakes, especially from California, are considered the best for collectors. The Chilean Atacama Desert provides large quantities of material, including rare manganese and nickel varieties, which are highly desirable in the collector's market.

Care and storage

## Cleaning The mineral is soluble in water, so **it must absolutely not be cleaned wet**. To remove dust and fine impurities, use only a soft, dry brush, a photographic air blower, or compressed air from a safe distance. ## What to Avoid Avoid all contact with water and chemical solutions, which can permanently damage or dissolve the specimen. The mineral is sensitive to changes in humidity – in overly dry air, it can dehydrate and crumble, and in overly humid conditions, it can "sweat" and slowly dissolve. Protect it from high temperatures and direct sunlight. ## Storage It is recommended to store specimens in stable conditions, preferably in closed, airtight containers (e.g., "membrane box" type) or in display cases that help maintain a constant humidity level. Keep them away from other minerals that may be hygroscopic.

Sources

IMA Mineral List (CNMNC)