Gismondine-Sr

Chemical formula: Sr₄(Si₈Al₈O₃₂)·₉H₂O

Gismondine-Sr is a very rare mineral from the zeolite group, a hydrated strontium aluminosilicate, forming microscopic, colorless crystals.

## Characteristics Gismondine-Sr is a hydrated strontium aluminosilicate and belongs to the zeolite group. It is the strontium analogue of gismondine-Ca. It forms very small, most often microscopic, colorless or white crystals, which usually occur as spherical or hemispherical aggregates. Individual crystals have a pseudo-octahedral or dipyramidal shape. ## Physical Properties Crystals exhibit a vitreous luster. Due to the small size of the crystals, most physical properties, such as hardness or density, have not been precisely determined for this mineral. ## History and Name The mineral's name refers to its chemical composition – it is a member of the gismondine series, in which strontium (Sr) is the dominant element. It was recognized by the International Mineralogical Association (IMA) in 2005. The type specimen (holotype) was found in the Kopeysk brown coal mine in the Chelyabinsk Oblast in the Urals, Russia.

Properties

Luster: Vitreous
Streak: White
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Identification of gismondine-Sr is possible only through advanced analytical methods, such as X-ray diffraction (XRD) and chemical microanalysis (EDS/WDS) to confirm the strontium-dominant composition. Visual identification in the field or in a collection is impossible due to its microscopic size and lack of characteristic macroscopic features. ## Distinguishing from Similar Minerals The mineral is visually indistinguishable from other zeolites forming similar spherical aggregates, such as gismondine-Ca, chabazite, phillipsite, or thomsonite. Differences can only be determined based on chemical and structural analysis. ## Crystal Forms It most often forms spherical or hemispherical aggregates up to 0.5 mm in diameter, composed of very small, radially arranged crystals. Individual crystals, visible under high magnification, have pseudo-octahedral or steep dipyramidal forms.

Geological environment

## Genesis It is a secondary mineral, formed as a result of low-temperature hydrothermal processes. At the type locality (Kopeysk mine), it was found in voids and fractures in burnt waste rock (coal shales) that underwent natural calcination due to an underground coal fire. ## Mineral Associations At the type locality in Russia, it coexists with Calcite, Aragonite, Anhydrite, Gypsum, Hematite, Quartz, and other zeolites, such as Thomsonite-Sr and Edingtonite. ## Localities The only confirmed and well-described locality for this mineral in the world is the Kopeysk brown coal mine, near Chelyabinsk in the Southern Urals, Russia.

Rarity

Extremely rare

For collectors

## Quality Criteria As a microscopic mineral, gismondine-Sr is valued exclusively by collectors specializing in rare minerals and "micromount" specimens. The value of a specimen is determined by the abundance of well-formed, spherical aggregates on the rock matrix and confirmation of identification through chemical analysis. The aesthetics of the specimen are of secondary importance.

Care and storage

## Cleaning Due to its extreme rarity and microscopic crystal size, gismondine-Sr specimens should not be cleaned mechanically or chemically. Any attempts at cleaning may destroy the delicate crystals. It is safest to leave the specimen in its original state. ## What to Avoid Avoid contact with any chemicals, acids, and detergents. Zeolites are sensitive to temperature changes, which can lead to dehydration and destruction of the crystal structure. The mineral should be protected from high temperatures and direct sunlight. ## Storage Specimens should be stored under stable conditions, in closed "micromount" containers, to protect them from dust, mechanical damage, and humidity changes. It is best to keep them away from heat and light sources.

Sources

IMA Mineral List (CNMNC)