Lokkaite-(Y)

Chemical formula: CaY<sub>4</sub>(CO<sub>3</sub>)<sub>7</sub>·9H<sub>2</sub>O

Lokkaite-(Y) is a rare, hydrated yttrium and calcium carbonate, forming small, spherical aggregates and rosettes with a silky luster.

## Characteristics Lokkaite-(Y) is a rare mineral from the carbonate group, chemically classified as a hydrated yttrium and calcium carbonate. It occurs as small, radial or spherulitic (spherical) aggregates, which can form rosettes. Individual crystals within these aggregates are typically microscopic, acicular (needle-like) or bladed, which gives the surface of specimens a characteristic fibrous texture. ## Physical Properties Lokkaite-(Y) crystals are very small and delicate. The mineral is characterized by a silky or pearly luster on the aggregate surfaces. It is a relatively soft and light mineral. ## Colors and Varieties Lokkaite-(Y) is most often colorless, white, or has a pale yellow tint. No color or commercial varieties are distinguished. ## History and Name The mineral was discovered in the Pyörönmaa pegmatite in Kangasala municipality, Finland. Its name, approved in 1970, honors Finnish chemist Lauri Lokka (1885–1966) for his contributions to the study of rare earth minerals in Finland. The suffix "-(Y)" indicates the dominance of yttrium in the chemical composition, in accordance with the naming rules for rare earth element minerals. ## Uses Due to its rarity and small crystal size, lokkaite-(Y) has no industrial applications. It is of purely scientific interest and is sought after by specialized collectors of rare minerals.

Properties

Mohs hardness
2-2.5
Luster
Pearly
Streak
White
Density
3.01
Cleavage
Good on {100}
Fracture
Uneven
Transparency
Translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Lokkaite-(Y) is identified by its characteristic mode of occurrence – as small, white or colorless, radial or spherical aggregates with a silky luster. Key to identification is the geological environment (granitic pegmatites) and co-occurrence with other rare earth minerals. Confirmation requires advanced analytical methods, such as X-ray diffraction (XRD) and chemical analysis (EDS/WDS). ## Distinguishing from Similar Minerals It can be confused with other secondary rare earth carbonates, such as tengerite-(Y) or kimuraite-(Y), which form similar white, fibrous coatings and aggregates. Distinguishing them "by hand" is practically impossible and requires laboratory analysis. They differ subtly in crystal structure and precise chemical composition. ## Crystal Forms It forms acicular or bladed crystals, which almost always occur as radial, fibrous, spherulitic (spherical), or rosette-like aggregates. Single, well-formed crystals are extremely rare and microscopic in size.

Geological environment

## Genesis Lokkaite-(Y) is a secondary mineral, formed by hydrothermal processes or weathering in alteration zones of granitic pegmatites rich in rare earth elements. It forms as a product of the alteration of earlier yttrium-bearing minerals, such as gadolinite-(Y) or allanite. ## Mineral Associations It most often co-occurs with minerals from which it forms or in whose company it crystallizes. Typical associated minerals include tengerite-(Y), kimuraite-(Y), gadolinite-(Y), allanite, bastnäsite-(Y), fluorite, quartz, and feldspars. ## Localities The most important and classic localities from which well-documented specimens originate are: - Pyörönmaa pegmatite, Kangasala, Finland (type locality). - St. Peters Dome Mine, Pikes Peak region, Colorado, USA. - Various localities in Norway, e.g., in the Tørdal area. - Specimens have also been found in pegmatites in Japan and Canada (e.g., Mont Saint-Hilaire).

Rarity

Very rare

For collectors

## Quality Criteria The collector's appeal of a lokkaite-(Y) specimen depends on several factors. Most important is the quality and definition of the spherulitic or rosette-like aggregates – the better formed and more distinct, the more valuable the specimen. The size of the aggregates and their abundance on the rock matrix are also important. Contrast with the color of the host rock can enhance aesthetic value. Specimens with well-studied associated minerals, especially other rare carbonates, are particularly desirable for specialized collections. ## Popular Localities Specimens from the type locality in Finland and from the Pikes Peak region in Colorado, USA, are considered the most classic and desirable. Specimens from Mont Saint-Hilaire in Canada are also valued due to the mineralogical diversity of this locality.

Care and storage

## Cleaning Due to its extreme delicacy and possible reactivity with water, mechanical cleaning or cleaning with liquids is highly inadvisable. The safest method for removing dust is to use a soft brush or carefully blow air from a safe distance. ## What to Avoid Avoid contact with water and all chemicals, including acids, which can dissolve it. The mineral is very soft and brittle, so it must be protected from any impact, scratching, or pressure. High temperatures should also be avoided, as they can cause water loss (dehydration) and destruction of the mineral's structure. ## Storage Lokkaite-(Y) specimens should be stored in stable conditions, in a closed, padded collector's box to protect them from mechanical damage, dust, and humidity changes. Do not expose it to direct sunlight.

Sources

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