thomasclarkite-(Y)

Chemical formula: NaY(HCO₃)(OH)₃ · 4H₂O

A rare hydrated sodium and yttrium bicarbonate, forming colorless, prismatic crystals, known only from one locality worldwide.

## Characteristics Thomasclarkite-(Y) is a very rare mineral from the carbonate group, chemically classified as a hydrated sodium and yttrium bicarbonate. It occurs as well-formed, prismatic crystals up to 2 mm long, which may be terminated pyramidally. The crystals are typically colorless to white and transparent. This mineral is found in small cavities within igneous rock. ## Physical Properties Thomasclarkite-(Y) is a very soft mineral, with a Mohs hardness of 2-3, meaning it can be scratched with a fingernail. It exhibits a vitreous luster and a white streak. It is relatively light, with a density of 2.30 g/cm³. It shows perfect cleavage in one direction, making it brittle and susceptible to mechanical damage. ## Colors and Varieties This mineral is typically colorless or white. No colored varieties or trade names are known. ## History and Name Thomasclarkite-(Y) was recognized as a new mineral species by the International Mineralogical Association (IMA) in 1997. Its name honors Thomas Henry Clark (1893–1996), a Canadian paleontologist and professor at McGill University in Montreal, in recognition of his contributions to the geology of the Mont Saint-Hilaire region. The suffix "-(Y)" indicates the dominance of yttrium in its chemical composition. ## Uses Due to its extreme rarity and small crystal sizes, thomasclarkite-(Y) has no industrial applications. It is solely of scientific and collector's interest.

Properties

Mohs hardness
2-3
Color
Honey-yellow to white
Luster
Vitreous
Streak
White
Density
2.30
Cleavage
Perfect on {010}.
Fracture
Irregular/Uneven
Transparency
Transparent,Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification Key diagnostic features include crystal habit (elongated prisms), perfect cleavage, low hardness (2-3 on the Mohs scale), and vitreous luster. It reacts with acids, effervescing vigorously, which is characteristic of carbonates. However, definitive identification requires advanced analytical methods such as spectroscopy or X-ray diffraction, due to its similarity to other minerals. ## Distinguishing from Similar Minerals Thomasclarkite-(Y) can be confused with other colorless, prismatic minerals found in the same locality, such as natrolite or other carbonates. Distinguishing it "by eye" is practically impossible. Chemical composition analysis (presence of yttrium) and physical properties are key. Unlike many zeolites, it reacts with acid. ## Crystal Forms It forms elongated, prismatic crystals with a bladed or acicular habit, reaching up to 2 mm in length. Crystals often occur as radial or randomly oriented aggregates in small vugs and rock fissures.

Geological environment

## Genesis Thomasclarkite-(Y) is a hydrothermal mineral. It forms in the late stage of crystallization in vesicles and fissures within alkaline intrusions, such as nepheline syenites. It crystallizes from solutions rich in sodium, yttrium, and carbonates at relatively low temperatures. ## Mineral Associations This mineral occurs in association with other rare minerals from Mont Saint-Hilaire. It is most commonly found with microcline, aegirine, quartz, petersenite-(Ce), remondite-(Ce), and mikkelsenite-(Y). ## Localities The only confirmed occurrence of thomasclarkite-(Y) worldwide is the Poudrette quarry, located on Mont Saint-Hilaire in the Montérégie region, Quebec, Canada. This is the type locality for this mineral.

Rarity

Extremely rare

For collectors

## Quality Criteria The most desirable specimens for collectors are those with well-formed, sharp, and transparent crystals that are clearly isolated on the rock matrix. Rich clusters of radial aggregates are highly valued. Contrast with a dark matrix (e.g., aegirine) also enhances the visual and collector's value of the specimen. Due to their microscopic size, specimen quality is assessed under magnification. ## Popular Localities The only source of specimens is the Poudrette quarry on Mont Saint-Hilaire, Canada. This locality is world-renowned for hundreds of mineral species, including many unique ones. Thomasclarkite-(Y) specimens are among the greatest rarities from this locality and are sought after by specialized collectors of rare minerals and microminerals.

Care and storage

## Cleaning Specimens should be cleaned with the utmost care, using compressed air to remove dust. Contact with water and any chemical agents should be avoided. Due to its low hardness, mechanical cleaning (e.g., with a brush) is highly inadvisable, as it can irreversibly damage or destroy the crystals. ## What to Avoid The mineral is very sensitive to acids, which cause its rapid decomposition. Contact with water, which can damage the crystal surface, should be avoided. It is brittle and sensitive to shocks and temperature changes. It should not be exposed to direct sunlight. ## Storage It is recommended to store specimens exclusively in specialized, sealed "micromount" boxes, which protect against dust, moisture, and mechanical damage. Display should be in stable conditions, away from sources of vibration and heat.

External references

Sources

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