Charmarite-3T

Chemical formula: Mn<sub>4</sub>Al<sub>2</sub>(OH)<sub>12</sub>CO<sub>3</sub>·3H<sub>2</sub>O

Charmaryite-3T is a very rare mineral from the hydrotalcite group, forming tiny, hexagonal, white or colorless crystals.

## Characteristics Charmaryite-3T is a hydrated manganese and aluminum carbonate, belonging to the hydrotalcite supergroup. It occurs as very small, platy crystals with a hexagonal outline, rarely exceeding 1 mm in size. These crystals often form rosette-like or spherical aggregates. It is a transparent to translucent mineral, white or colorless, with a characteristic pearly luster on cleavage surfaces. ## Physical Properties This mineral is very soft, with a Mohs hardness of only 2. It has a pearly luster on cleavage planes and a vitreous luster on other faces. The calculated density is approximately 2.58 g/cm³. It is light and brittle. ## Colors and Varieties Charmaryite-3T is usually colorless or white. No colored or commercial varieties have been distinguished. ## History and Name The name "charmaryite" comes from the names of Charles (1912-2004) and Mabel (1914-1991) Sternberg, prominent mineral collectors from Connecticut, USA. The suffix "-3T" refers to its trigonal symmetry and three-layer unit cell (3T polytype). The mineral was approved by the IMA in 2000, and its description was published in 2003. It was discovered in the mine dumps of Mont Saint-Hilaire in Canada. ## Uses Due to its extreme rarity and microscopic crystal size, charmaryite-3T has no industrial applications. It is solely an object of interest for specialized collectors of rare minerals and scientists.

Properties

Mohs hardness
2
Luster
Pearly, Vitreous
Streak
White
Density
2.58
Cleavage
Perfect on {0001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Trigonal

Diagnostic features

## Identification Charmaryite-3T is difficult to identify without specialized equipment. Its characteristic features include its occurrence as small, hexagonal, white or colorless plates with a pearly luster. A key reaction is with hydrochloric acid – the mineral effervesces violently. However, definitive identification requires advanced methods such as X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with other minerals from the hydrotalcite group, such as quintinite or manasseite, which form similar hexagonal crystals. Distinguishing it from them is practically impossible without chemical analysis or XRD. It differs from calcite or dolomite by its much lower hardness and pearly luster. ## Crystal Forms It forms thin, platy crystals with a hexagonal outline. These crystals often combine into rosette-like, fan-shaped, or spherulitic aggregates, growing on other minerals.

Geological environment

## Genesis Charmaryite-3T is a secondary mineral, formed in the late stages of hydrothermal processes in complex, alkaline nepheline syenite intrusions. It forms in rock cavities and fissures, crystallizing from solutions rich in manganese, aluminum, and carbonates. ## Mineral Associations At its type locality (Mont Saint-Hilaire), it co-occurs with many other rare minerals, such as quartz, microcline, aegirine, rhodochrosite, analcime, natrolite, petersenite-(Ce), catapleiite, and sérandite. ## Localities The only confirmed and well-documented occurrence of charmaryite-3T in the world is the Poudrette quarry in Mont Saint-Hilaire, Montérégie region, Quebec province, Canada. This is its type locality.

Rarity

Extremely rare

For collectors

## Quality Criteria The most prized charmaryite-3T specimens are those with well-formed, sharp, and clearly visible crystals or their aesthetic aggregates. Due to their microscopic size, the quality of the crystal itself (transparency, luster) and its placement on the rock matrix are crucial. Contrast with associated minerals, such as dark aegirine or pink rhodochrosite, significantly enhances the specimen's attractiveness. Specimens with crystals exceeding 0.5 mm are considered exceptional. ## Popular Localities The only source of collector specimens is the Poudrette quarry in Mont Saint-Hilaire, Canada. This locality is world-renowned for hundreds of rare and unique minerals, and specimens from there are highly valued by collectors specializing in systematics or rare minerals.

Care and storage

## Cleaning Charmaryite-3T specimens should be handled with the utmost care. Due to its extreme softness and brittleness, mechanical cleaning is not recommended. If absolutely necessary, compressed air (from a safe distance) can be used to remove loose dust. Contact with water, which can damage the delicate crystals, should be avoided. ## What to Avoid This mineral is sensitive to acids, which cause it to effervesce violently and decompose. All chemicals, ultrasound, and sudden temperature changes should be avoided. The crystals are very brittle and susceptible to mechanical damage, even with the lightest touch. ## Storage Specimens should be stored under stable conditions, in closed, padded "micromount" boxes to protect them from dust, moisture, and physical damage. They should not be exposed to direct sunlight or temperature fluctuations.

Sources

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