Strontiodresserite

Chemical formula: SrAl<sub>2</sub>(CO<sub>3</sub>)<sub>2</sub>(OH)<sub>4</sub>·H<sub>2</sub>O

Strontiodresserite is a rare mineral from the carbonate group, forming small, spherical aggregates of white or colorless hue.

## Characteristics Strontiodresserite is a hydrated strontium and aluminum carbonate. It occurs extremely rarely, forming tiny, spherical or hemispherical aggregates with a radial internal structure. Individual crystals are in the form of lamellae or needles and reach sizes below 1 mm, making them visible only under high magnification. It typically forms thin coatings and crusts on rock surfaces. ## Physical properties Strontiodresserite crystals are very brittle. This mineral is characterized by a silky or pearly luster on the surfaces of aggregates, while on the faces of individual crystals, the luster is vitreous. It is a light mineral, with a density of approximately 3.02 g/cm³. ## Colors and varieties Strontiodresserite is most often colorless or white. No color or commercial varieties are distinguished. ## History and name The mineral was discovered in the Francon Quarry in Montreal (Quebec, Canada) and described in 1977. Its name refers to its chemical composition (dominant strontium) and is an acknowledgment of John Alexander Dresser (1866-1954), a Canadian geologist who made significant contributions to the study of Quebec's geology. It is the strontium analogue of dresserite. ## Uses Strontiodresserite has no industrial application. It is of scientific and collector's interest only as a very rare mineral.

Properties

Mohs hardness
4
Luster
Vitreous, Pearly, Silky
Streak
White
Density
3.02
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Strontiodresserite is recognized by its characteristic mode of occurrence – small, white spheres (spherulites) with a silky luster, deposited on the host rock. A key diagnostic feature is its vigorous reaction with hydrochloric acid, which confirms its belonging to the carbonates. However, definitive identification requires advanced research methods, such as X-ray diffraction (XRD) or chemical analysis (EDS). ## Distinguishing from similar minerals It can be confused with other white carbonates occurring in similar parageneses, such as dresserite, hydrocerussite, or weloganite. Dresserite is its barium analogue, and distinguishing it is practically only possible through chemical analysis. Weloganite usually forms better-developed, hexagonal crystals. Hydrocerussite often exhibits fluorescence under UV light, which strontiodresserite does not possess. ## Crystal forms This mineral forms microscopic, platy crystals that combine into radial, spherical, or hemispherical aggregates (spherulites) up to 2 mm in diameter.

Geological environment

## Genesis Strontiodresserite is a secondary mineral, forming under low-temperature hydrothermal conditions. It occurs in vugs and fractures within alkaline igneous intrusions, such as nepheline syenites and carbonatites. It forms as a result of the alteration of pre-existing minerals. ## Mineral associations It most commonly co-occurs with quartz, weloganite, dresserite, dawsonite, analcime, as well as other rare minerals found in the Francon Quarry. ## Localities The most important and classic locality for strontiodresserite is the Francon Quarry in Montreal, Quebec, Canada, where it was discovered. This is the type locality from which most known specimens originate. It has also been reported in the Mont Saint-Hilaire alkaline complex, also in Quebec.

Rarity

Very rare

For collectors

## Quality criteria The most highly valued strontiodresserite specimens are those that possess numerous, well-formed, and undamaged spherulites, clearly standing out from the host rock (matrix). Color contrast with the background and co-occurrence with other rare minerals from the same locality, e.g., weloganite, significantly increase the specimen's collector value. Due to the microscopic size of the crystals, the size of the aggregates themselves is a key factor. ## Popular localities The only source of valuable collector specimens is the Francon Quarry in Montreal (Quebec, Canada). This is a closed and no longer accessible locality, which makes material from this site highly sought after in the collector's market.

Care and storage

## Cleaning Specimens should be cleaned only very carefully, using compressed air to remove dust. Contact with water is not recommended due to the risk of damaging delicate aggregates. Ultrasonic cleaners should be avoided. ## What to avoid Contact with acids must be strictly avoided, as they cause violent effervescence and decomposition of the mineral. Brittle aggregates are very sensitive to any impacts and vibrations. It should be protected from moisture. ## Storage It is recommended to store specimens in closed, padded collector's boxes to protect them from dust, mechanical damage, and changes in humidity.

Sources

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