Keiviite-(Y)

Chemical formula: Y₂Si₂O₇

Keiviite-(Y) is a rare yttrium silicate, forming colorless or white, small crystals with a vitreous luster.

## Characteristics Keiviite-(Y) is a mineral belonging to the silicate group, specifically an yttrium sorosilicate. It occurs as very small, prismatic or tabular crystals, rarely exceeding 1 mm in length. It typically forms radial aggregates or appears as single, dispersed crystals. It is colorless to white, sometimes with a yellowish or pinkish tint. ## Physical Properties This mineral is characterized by a hardness of 4-5 on the Mohs scale and a density of approximately 4.47 g/cm³. It has a vitreous luster and is transparent to translucent. It does not exhibit cleavage, and its fracture is uneven. ## Colors and Varieties Keiviite-(Y) is typically colorless or white. Some specimens may have a pale yellow or pinkish hue. No distinct color varieties or commercial varieties are recognized. ## History and Name The name "keiviite" refers to its discovery location – the Keivy Massif on the Kola Peninsula in Russia. The suffix "-(Y)" in the name indicates the dominant rare-earth element in its composition, which is yttrium. The mineral was described and approved as a new mineral species in 1986. ## Uses Due to its rarity and small crystal size, keiviite-(Y) has no industrial applications. It is of purely scientific and collector's interest, being an object of fascination for specialized collectors of rare-earth minerals.

Properties

Mohs hardness: 4-5
Luster: Vitreous
Streak: White
Density: 4.47
Cleavage: None
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Field identification of keiviite-(Y) is practically impossible due to its small size and resemblance to other minerals, such as quartz or feldspars. Definitive identification requires advanced laboratory methods, such as chemical composition analysis (EDS) or X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with other yttrium silicates, such as thortveitite, with which it often co-occurs. Thortveitite crystallizes in the monoclinic system and has different optical properties. It is distinguished from quartz and feldspars by its significantly higher density. ## Crystal Forms It forms elongated, prismatic or flattened, tabular crystals. It often occurs as radial or randomly oriented aggregates on the surface of the host rock.

Geological environment

## Genesis Keiviite-(Y) forms in the late stages of crystallization of alkaline pegmatites, rich in rare-earth elements. It develops in vugs and fractures within these rocks. ## Mineral Associations This mineral co-occurs with other rare-earth minerals. It is most commonly associated with albite, microcline, quartz, aegirine, fluorite, thortveitite, gadolinite-(Y), and xenotime-(Y). ## Localities The most important and best-documented locality, which is also the type locality, is the Keivy Massif on the Kola Peninsula in Russia. It is also known from several other worldwide localities, including pegmatites in Norway (e.g., in the Tysfjord region).

Rarity

Very rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with well-formed, sharp, and transparent crystals, forming aesthetic groups on a contrasting rock matrix. Due to their small size, the microscopic quality of the crystals is crucial. The size and richness of the aggregate significantly increase the specimen's value. ## Popular Localities Undoubtedly, the most sought-after specimens come from the type locality – the Keivy Massif in Russia. These are considered the global standard for this mineral.

Care and storage

## Cleaning It is recommended to clean only with compressed air to remove dust. Due to the small size and fragility of the crystals, avoid contact with water and brushes, which could damage them or dislodge them from the rock matrix. ## What to Avoid Avoid ultrasonic cleaners, chemical agents, and sudden temperature changes. The mineral is susceptible to mechanical damage. ## Storage Specimens should be stored in stable conditions, in sealed "micromount" boxes, to protect them from dust and mechanical damage. It is not sensitive to light.

Sources

IMA Mineral List (CNMNC)