Mckelveyite-(Y)

Chemical formula: NaBa<sub>3</sub>CaY(CO<sub>3</sub>)<sub>6</sub>·3H<sub>2</sub>O

Mckelveyite-(Y) is a rare, hydrated mineral from the carbonate group, forming characteristic, platy crystals in shades of yellow and green.

## Characteristics Mckelveyite-(Y) is a complex, hydrated carbonate of sodium, barium, calcium, and yttrium. It forms very small, thin, platy crystals with a pseudohexagonal outline. These crystals almost always occur as radial or spherical aggregates resembling rosettes, whose diameter rarely exceeds a few millimeters. Due to their habit and small size, specimens are usually admired under magnification. ## Physical Properties This mineral is characterized by a hardness in the range of 3.5-4 on the Mohs scale, making it relatively soft. It has a vitreous luster, which becomes pearly on cleavage surfaces. It is transparent to translucent. The density is approximately 3.5-3.6 g/cm³. ## Colors and Varieties Typical colors of mckelveyite-(Y) are pale yellow, greenish-yellow, and green. The name with the "-(Y)" suffix indicates that yttrium (Y) is the dominant rare earth element in its structure. There is also an analog with neodymium dominance, mckelveyite-(Nd), which is much rarer. ## History and Name The mineral was first described in 1965. Its name honors Vincent Ellis McKelvey (1916-1987), an American geologist and former director of the United States Geological Survey (USGS). The suffix "-(Y)" was added in 1987 as part of the standardization of rare earth mineral nomenclature. ## Uses Mckelveyite-(Y) has no industrial applications. It is of purely scientific and collector's interest as a rare and interesting mineral.

Properties

Mohs hardness
3.5-4
Luster
Vitreous to Pearly
Streak
White
Density
3.5-3.6
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Transparent to Translucent
Crystal system
Triclinic

Diagnostic features

## Identification The most important diagnostic feature of mckelveyite-(Y) is its characteristic occurrence in the form of small, radial rosettes composed of platy crystals. Its yellow-green color, excellent cleavage, and specific environment of occurrence in oil shales are also helpful. ## Distinguishing from Similar Minerals Mckelveyite-(Y) is sometimes confused with other rare carbonates from the same locality, especially ewaldite. However, ewaldite crystallizes in the hexagonal system and forms dipyramidal crystals, not platy rosettes. Final and certain distinction of these minerals often requires chemical or crystallographic analysis. ## Crystal Forms Crystals are thin, platy, with a hexagonal outline. They are almost always intergrown into spherical or hemispherical aggregates and rosettes. Single, isolated crystals are rare.

Geological environment

## Genesis Mckelveyite-(Y) is an authigenic mineral, meaning it crystallizes in situ (at the place of rock formation) under low-temperature conditions. It forms in a strongly alkaline environment within lacustrine sediments, specifically in dolomitic oil shales of the Green River Formation. ## Mineral Associations This mineral co-occurs with other rare evaporite and authigenic minerals, such as ewaldite, shortite, northupite, searlesite, as well as quartz, pyrite, and dolomite. ## Localities The most important and well-known locality for mckelveyite-(Y) in the world is the Green River Formation, especially in Sweetwater County, Wyoming, USA. All the best collector specimens come from there. Other localities, such as the Kola Peninsula in Russia, are of marginal importance.

Rarity

Very rare

For collectors

## Quality Criteria The most highly valued mckelveyite-(Y) specimens are those with sharp, well-defined rosettes of intense yellow or green color. The size of the aggregates is of great importance – specimens exceeding 5 mm in diameter are considered exceptional. The attractiveness is enhanced by the placement of the rosettes on a contrasting rock matrix or their co-occurrence with other rare minerals from the Green River Formation. ## Popular Localities The only source of collector-grade specimens is the Green River Formation in Wyoming, USA. Specimens from this locality are classic and standard for this mineral species.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush and distilled water at room temperature. Avoid strong water jets, which could damage delicate aggregates. ## What to Avoid As a carbonate, mckelveyite-(Y) is sensitive to acids, which cause its rapid dissolution. Avoid contact with any chemicals. It is a hydrated mineral, so it should not be heated or stored in very dry conditions, which could lead to water loss and structural damage. Due to its low hardness, it is susceptible to scratching. ## Storage It is recommended to store specimens in closed, padded boxes to protect them from dust, mechanical damage, and sudden changes in humidity. Do not expose it to prolonged direct sunlight.

External references

Sources

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