Caysichite-(Y)
Chemical formula: (Ca,Yb,Er)₄Y₄Si₈O₂₀(CO₃)₆(OH)·7H₂O
A rare yttrium and calcium silicate, forming radial aggregates of acicular, white or yellowish crystals with a silky luster.
Properties
- Mohs hardness
- 4.5
- Color
- Colourless, white, pale yellow, rarely greenish
- Luster
- Silky to vitreous
- Streak
- White
- Density
- 3.03
- Cleavage
- Perfect on {010}
- Fracture
- Uneven
- Transparency
- Transparent,Translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification A characteristic feature of caysichite-(Y) is its occurrence in the form of radial or spherical aggregates composed of very fine, acicular crystals. Silky luster, light color (white, yellowish), and co-occurrence with other rare earth minerals in granitic pegmatites are key indicators. ## Distinguishing from Similar Minerals Caysichite-(Y) can be confused with other fibrous secondary minerals, such as some zeolites (e.g., natrolite) or hemimorphite. It is distinguished from zeolites by its higher density and environment of occurrence (pegmatites with rare earth minerals). Hemimorphite often forms fan-shaped or botryoidal aggregates, but rarely such delicate, acicular aggregates as caysichite-(Y). Final distinction requires advanced analytical methods (XRD, EDS). ## Crystal Forms Crystals are elongated, acicular or hair-like, crystallizing in the orthorhombic system. They almost always occur as radial, stellate, or spherulitic aggregates. Single, well-formed crystals are extremely rare.
Geological environment
## Genesis Caysichite-(Y) is a secondary mineral, formed in the late stages of hydrothermal processes or as a result of weathering of primary minerals in granitic pegmatites rich in rare earth elements. It forms in rock cavities and fissures. ## Mineral Associations This mineral often co-occurs with other rare earth minerals, such as xenotime, gadolinite, allanite, as well as with quartz, microcline, albite, fluorite, beryl, and tengerite-(Y). ## Localities The most important and type locality, from which the best specimens originate, is the Evans-Lou mine in Val-des-Monts, Quebec, Canada. It has also been reported in several other localities worldwide, including pegmatites in Norway (e.g., in the Tørdal area), Sweden (Östanmossa mine), and Italy (Baveno).
Rarity
Very rare
For collectors
## Quality Criteria The most valued by collectors are specimens with well-formed, spherical or radial aggregates of intense yellow color, contrasting with the dark matrix rock. The absence of damage to the delicate, acicular crystals is also important. Due to its small size, caysichite-(Y) is primarily a mineral for micromount collections. ## Popular Localities By far the most sought-after specimens, considered the global standard for this mineral, come from its type locality – the Evans-Lou mine in Quebec, Canada.
Care and storage
## Cleaning Specimens should be cleaned very carefully, using a soft brush to remove dust. Due to possible reactivity with acids, all chemical cleaning agents should be avoided. If water is necessary, it should be distilled water, and the specimen should be dried quickly and thoroughly. ## What to Avoid Avoid contact with acids, which can react with the carbonate part of the mineral, causing damage. The mineral is relatively soft, so it must be protected from scratching by harder minerals. Ultrasonic cleaners and steam cleaning should also be avoided. ## Storage Collections of caysichite-(Y), especially delicate, acicular aggregates, are best stored in sealed "micromount" boxes, which protect them from dust, mechanical damage, and sudden changes in humidity.