Ewaldite

Chemical formula: BaCa(CO₃)₂·2.6H₂O

Ewaldite is a rare, hydrated barium and calcium carbonate, forming small, hexagonal crystals of white or colorless hue.

## Characteristics Ewaldite is a hydrated barium and calcium carbonate, occurring extremely rarely. It forms small, hexagonal, prismatic or tabular crystals, which rarely exceed 1 mm in size. It is usually observed as small aggregates, rosettes, or as single, scattered crystals on the surface of other minerals. It is colorless to white and typically transparent. ## Physical Properties This mineral is characterized by a Mohs hardness of approximately 3. It has a vitreous luster and is transparent. The density of ewaldite is approximately 3.33 g/cm³. It is brittle and exhibits perfect cleavage in one direction. ## Colors and Varieties Ewaldite is an idiochromatic mineral, meaning its chemical composition determines its color. It is colorless or white. No named varieties of this mineral are distinguished. ## History and Name The mineral's name honors Paul Peter Ewald (1888-1985), a German physicist and crystallographer, a pioneer in X-ray diffraction and crystal structure research. Ewaldite was first described in 1971 based on material found in the Green River Formation in Wyoming, USA. ## Uses Due to its extreme rarity and small crystal size, ewaldite has no industrial applications. It is solely an object of scientific and collecting interest for specialized collectors of rare minerals.

Properties

Mohs hardness
3
Color
Bluish green, pale greenish gray
Luster
Vitreous
Streak
White
Density
3.25
Cleavage
Perfect on {0001}
Fracture
Conchoidal
Transparency
Translucent
Crystal system
Hexagonal

Diagnostic features

## Identification Amateur identification of ewaldite is practically impossible. It requires advanced analytical methods, such as X-ray diffraction (XRD) or Raman spectroscopy. A preliminary indication may be its co-occurrence with other rare evaporite minerals in the specific geological environment of the Green River Formation. ## Distinguishing from Similar Minerals Ewaldite can be confused with other colorless carbonates, such as weloganite, mckelveyite-(Y), or shortite, with which it often co-occurs. Differentiation requires specialized laboratory tests, as visual features (crystal form, color) are very similar. ## Crystal Forms Ewaldite crystallizes in the hexagonal system, forming six-sided, pyramidal or tabular crystals. They often occur as small, radial aggregates or rosettes.

Geological environment

## Genesis Ewaldite is an evaporite mineral. It forms under unique low-temperature conditions, in highly saline, alkaline lakes. It crystallizes directly from solutions rich in barium, calcium, and carbonates within clay sediments and oil shales. ## Mineral Associations This mineral co-occurs with other rare evaporite minerals characteristic of the Green River Formation. The most common associations include: shortite, mckelveyite-(Y), weloganite, norsethite, loughlinite, and labuntsovite. ## Localities The only confirmed and most important occurrence of ewaldite in the world is the Green River Formation, specifically the trona deposits in Sweetwater and Uintah counties in Wyoming and Utah, USA. This is the type locality for this mineral.

Rarity

Very rare

For collectors

## Quality Criteria The most highly valued ewaldite specimens are those with sharply terminated, well-formed, and transparent crystals, clearly standing out from the matrix. Due to the microscopic size of the crystals, their sharpness and lack of damage, visible under magnification, are crucial. Rich aggregates or associations with other rare minerals from this locality are particularly desirable. ## Popular Localities All valuable collector specimens of ewaldite come from a single region - the trona mines in the Green River Basin in Wyoming, USA. Specimens from this locality are the global standard for this mineral.

Care and storage

## Cleaning Ewaldite specimens should be cleaned with the utmost care, using only compressed air to remove dust. Due to its reactivity with acids and potential solubility, contact with water and all chemical agents should be avoided. ## What to Avoid Contact with acids, which cause its rapid dissolution with the release of carbon dioxide, must be absolutely avoided. The mineral is sensitive to high temperatures and can undergo dehydration. It should be protected from moisture and temperature changes. ## Storage It is recommended to store ewaldite specimens in stable conditions, in closed, airtight containers (so-called "membrane box" or "perky box"), to protect them from mechanical damage, dust, and humidity changes.

External references

Sources

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