Churchite-(Y)

Chemical formula: Y(PO₄)·2H₂O

Churchite-(Y) is a rare, hydrated yttrium phosphate, forming characteristic radial aggregates of tiny, acicular crystals.

## Characteristics Churchite-(Y) is a hydrated yttrium phosphate, belonging to the group of rare minerals. It most often occurs as small, radial or stellate aggregates, which consist of very tiny, acicular or bladed crystals. These aggregates form crusts and coatings on host rocks, and less frequently occur as earthy or powdery masses. Individual crystals are usually too small to be observed without magnification. ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 3. It is brittle and has perfect cleavage in one direction. The luster on crystal surfaces is vitreous, and on cleavage planes it can be pearly. Earthy varieties are dull. It is a light mineral, with a density of approximately 3.14-3.27 g/cm³. ## Colors and Varieties Churchite-(Y) is most often colorless, white, or grayish-white. Sometimes it is tinted with delicate yellowish or pinkish hues, which is caused by impurities. There are no named color or commercial varieties. ## History and Name The mineral was first described in 1865. Its name comes from Arthur Herbert Church (1834-1915), a British chemist and mineralogist, who first performed its chemical analysis. The suffix "-(Y)" was added later in accordance with the rules for naming rare earth minerals, to indicate that yttrium (Y) is the dominant element in this group. ## Uses Churchite-(Y) has no industrial applications. It is solely an object of scientific interest and is valued by collectors of rare minerals.

Properties

Mohs hardness
3
Luster
Vitreous to Pearly
Streak
White
Density
3.14-3.27
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent to Translucent
Crystal system
Monoclinic

Diagnostic features

## Identification The most characteristic feature of churchite-(Y) is its mode of occurrence - radial aggregates composed of tiny, acicular crystals. Identification is also aided by its low hardness (3 on the Mohs scale), perfect cleavage, and typical environment of occurrence, i.e., oxidation zones of ore deposits. The luster can be vitreous or pearly on cleavage surfaces. ## Distinguishing from Similar Minerals Churchite-(Y) can be confused with other minerals that form radial aggregates. - **Wavellite** has a very similar appearance but is harder (3.5-4) and is an aluminum phosphate, not yttrium. - **Gypsum** in acicular form is much softer (hardness 2). - **Hemimorphite** forms similar aggregates but is much harder (4.5-5) and is a zinc silicate. ## Crystal Forms Crystals are monoclinic, acicular or bladed. They almost always occur in radial, stellate, or fan-shaped aggregates. They also form thin crusts and coatings, less frequently powdery or earthy masses.

Geological environment

## Genesis Churchite-(Y) is a secondary mineral. It forms in oxidation zones (gossans) of ore deposits, in hydrothermal veins, and in granitic pegmatites. It forms as a result of weathering and alteration of primary minerals rich in yttrium and other rare earth elements, such as xenotime-(Y) or gadolinite. ## Mineral Associations It often co-occurs with other secondary phosphate minerals and iron oxides. The most common associated minerals include: limonite, goethite, wavellite, variscite, strengite, pharmacosiderite, as well as quartz and feldspars. ## Localities It is a rare mineral, known from several dozen localities worldwide. The type locality, from which historical specimens originate, is in Cornwall (United Kingdom). Other significant occurrences have been noted in Wales, Bavaria (Germany), Portugal, the Czech Republic (near Jáchymov), and the United States (North Carolina and Virginia).

Rarity

Rare

For collectors

## Quality Criteria The collector appeal of churchite-(Y) specimens depends primarily on the richness and aesthetics of the aggregates. The most valued specimens are those where the radial aggregates are well-formed, densely cover the rock matrix, and are undamaged. The size of individual "stars" or "fans" is also important. The color, usually white or colorless, is a secondary factor. ## Popular Localities Specimens from historical localities in Cornwall, United Kingdom, are considered classic and most desirable. Good quality material also comes from some pegmatites in Germany and the United States.

Care and storage

## Cleaning Churchite-(Y) specimens are very delicate and brittle. Only a soft brush should be used to remove dust and loose contaminants. If necessary, the specimen can be rinsed in distilled water and then left to dry completely at room temperature. Ultrasonic cleaners should not be used, as they can damage the tiny crystals. ## What to Avoid The mineral is sensitive to acids. As a hydrated mineral, it is also susceptible to structural changes under high temperatures, which can lead to its dehydration and destruction. It should be protected from impacts and contact with harder minerals that could scratch or damage it. ## Storage It is recommended to store specimens in separate, padded collector boxes to prevent abrasions and mechanical damage. Avoid areas with high humidity or those exposed to sudden temperature changes.

Sources

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