Ashcroftine-(Y)

Chemical formula: K<sub>5</sub>Na<sub>5</sub>Y<sub>12</sub>Si<sub>28</sub>O<sub>70</sub>(OH)<sub>2</sub>(CO<sub>3</sub>)<sub>8</sub>·8H<sub>2</sub>O

A rare potassium, sodium, and yttrium silicate, forming pink, prismatic crystals with a silky luster, found in syenitic pegmatites.

## Characteristics Ashcroftine-(Y) is a complex, hydrated potassium, sodium, and yttrium silicate with additional carbonate and hydroxyl groups. This mineral forms characteristic, elongated, prismatic crystals, often occurring in radial or fibrous aggregates. Its most typical visual features are a delicate, pink color and a silky luster on the crystal surfaces. ## Physical Properties Ashcroftine-(Y) has a hardness of approximately 5 on the Mohs scale. It exhibits a vitreous to silky luster, especially on cleavage surfaces. It is a translucent mineral. Its density is about 2.9 g/cm³. ## Colors and Varieties This mineral typically occurs in shades from pale pink to pink. No distinct color varieties or commercial varieties have been identified. ## History and Name The mineral's name honors Frederick Noel Ashcroft (1878–1949), a British mineral collector who amassed a significant collection, now housed at the Natural History Museum in London. The mineral was first described in 1933 by M.H. Hey and F.A. Bannister. The suffix "-(Y)" in the name indicates the dominance of yttrium in its chemical composition. ## Uses Ashcroftine-(Y) has no industrial applications. It is solely an object of interest for collectors of rare minerals and a subject of scientific research due to its complex structure and chemical composition.

Properties

Mohs hardness
5
Luster
Vitreous, Silky
Streak
White
Density
2.9
Cleavage
Good on {100} and {010}
Fracture
Uneven
Transparency
Translucent
Crystal system
Tetragonal

Diagnostic features

## Identification Ashcroftine-(Y) can be identified by its characteristic pink color, prismatic crystal habit, and occurrence in radial aggregates. The silky luster and relatively low hardness (around 5) are also helpful features. However, its association with a specific geological environment – syenitic pegmatites – is key. ## Distinguishing from Similar Minerals This mineral can be confused with other pink zeolitic minerals or fibrous silicates, such as natrolite or thomsonite. Ashcroftine-(Y) differs from them by its crystal habit (square in cross-section), higher density, and unique chemical composition, rich in yttrium. Final differentiation requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms Crystals are elongated, prismatic, with a square cross-section. They typically form radial, stellate, or fibrous clusters and aggregates.

Geological environment

## Genesis Ashcroftine-(Y) is a hydrothermal mineral. It forms in the late stages of crystallization in nepheline syenite pegmatites, filling voids and fractures in the rock. Its presence indicates an environment rich in rare earth elements, especially yttrium. ## Mineral Associations This mineral co-occurs with other minerals typical of syenitic pegmatites, such as microcline, nepheline, aegirine, eudialyte, lorenzenite, catapleiite, and various minerals from the zeolite group. ## Localities The most important and classic locality (type locality) for ashcroftine-(Y) is the Narsarsuk (Narssârssuk) alkaline complex in Greenland. This is the primary location from which the best-formed specimens originate. The mineral has also been identified in the Mont Saint-Hilaire complex in Quebec, Canada, which is known for its occurrence of many rare alkaline minerals.

Rarity

Very rare

For collectors

## Quality Criteria Specimens with well-formed, sharp crystals of intense pink coloration are most valued by collectors. Radial aggregates forming aesthetic, stellate shapes on the rock matrix are particularly sought after. Crystal size, luster, and lack of mechanical damage significantly increase the collector's value of a specimen. ## Popular Localities Undoubtedly, the most desirable and classic specimens come from Narsarsuk, Greenland. Material from Mont Saint-Hilaire, Canada, is also prized, although it often occurs in the form of smaller crystals.

Care and storage

## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Due to possible water sensitivity, prolonged soaking should be avoided. If liquid is necessary, isopropyl alcohol is recommended, followed by quick drying. ## What to Avoid Avoid contact with acids and other aggressive chemicals that can damage the mineral. It should not be heated or subjected to ultrasound. Prolonged exposure to direct sunlight may potentially cause color fading. ## Storage Ashcroftine-(Y) specimens are fragile and should be stored in separate, padded boxes to prevent mechanical damage and abrasion. They should be protected from dust and moisture.

External references

Sources

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