Yttrocrasite-(Y)

Chemical formula: (Y,Th₄+,Ca,U₆+,U₄+)(Ti₄+,Fe₃+)₂(O,OH)₆

Yttrocrasite-(Y) is a rare, radioactive oxide mineral containing yttrium and titanium, forming black, resinous masses and prismatic crystals.

## Characteristics Yttrocrasite-(Y) is a complex oxide belonging to the euxenite group. It occurs as elongated, prismatic crystals with a square cross-section, often terminated by pyramids. It also forms granular aggregates and massive forms. It is usually opaque, black or brownish-black, with a pitchy (resinous) to vitreous luster. Due to its thorium and uranium content, this mineral is highly radioactive. Over time, it undergoes metamictization, which is the destruction of its crystal lattice due to its own radiation, leading to the loss of its original structure and changes in physical properties. ## Physical Properties The mineral is characterized by a hardness of 5.5-6.5 on the Mohs scale and a significant density, ranging from 4.8 to 5.5 g/cm³, which is typical for minerals containing heavy elements. The luster is resinous to almost metallic on fresh surfaces. The fracture is conchoidal to uneven. It is brittle. ## Colors and Varieties Yttrocrasite-(Y) occurs in uniform colors – from brownish-black to completely black. No color or commercial varieties are distinguished. ## History and Name The mineral's name, given in 1906 by William E. Hidden and Charles H. Warren, refers to its chemical composition and structure. The first part, "yttro-", comes from the element yttrium (Y), and the second, "-crasite" (from Greek κρᾶσις - "mixture"), refers to its complex chemical composition. The suffix "-(Y)" was added later in accordance with rare-earth mineral nomenclature rules, indicating the dominant element in this group. The mineral was discovered in a feldspar mine in Burnet County, Texas, USA. ## Uses Due to its rarity and radioactivity, yttrocrasite-(Y) has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals, pegmatite minerals, or radioactive minerals.

Properties

Mohs hardness: 5.5 - 6.5
Luster: Resinous to pitchy
Streak: Brownish-gray to black
Density: 4.8 - 5.5
Cleavage: Indistinct/None
Fracture: Conchoidal to uneven
Transparency: Opaque
Crystal system: Orthorhombic

Diagnostic features

## Identification A key diagnostic feature of yttrocrasite-(Y) is its strong radioactivity, which can be easily detected with a Geiger counter. Other helpful identification features include its black color, resinous luster, high density, prismatic crystal habit, and occurrence in granitic pegmatites. The mineral is often metamict, meaning its internal crystal structure has been destroyed by its own radiation. ## Distinguishing from Similar Minerals Yttrocrasite-(Y) can be confused with other black, radioactive minerals from pegmatites, such as euxenite, samarskite, fergusonite, or uraninite. Euxenite-(Y) has very similar properties, and a definitive distinction often requires chemical analysis (EDS/WDS) or X-ray diffraction (XRD), especially since yttrocrasite-(Y) is often intergrown with it. Samarskite and fergusonite usually have a more vitreous or metallic luster. Uraninite crystallizes in the isometric system, forming cubic crystals, and is significantly denser. ## Crystal Forms Crystals are typically prismatic, elongated along the [001] axis, with a roughly square cross-section. They often exhibit simple terminations or are terminated by pyramid faces. It also occurs as granular aggregates or irregular masses embedded in the host rock.

Geological environment

## Genesis Yttrocrasite-(Y) is a mineral of magmatic origin, crystallizing in the late stages from residual melts rich in rare earth elements, titanium, niobium, thorium, and uranium. It forms in granitic pegmatites, especially those of syenitic and nepheline-syenitic character. ## Mineral Associations This mineral co-occurs with other minerals typical of granitic pegmatites, such as quartz, microcline, albite, biotite, and muscovite. Its direct associates often include other rare minerals, including zircon, euxenite-(Y), fergusonite-(Y), allanite, gadolinite, monazite, thorianite, and uraninite. ## Localities The most important and historical occurrences of yttrocrasite-(Y) are: - **USA**: Burnet County and Llano County in Texas (type locality); Jefferson County in Colorado. - **Norway**: Vest-Agder county, especially around Iveland and Evje og Hornnes, known for numerous granitic pegmatites. - **Sweden**: Ytterby mine near Stockholm, a historical site for the discovery of many rare earth elements.

Rarity

Very rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with well-formed, sharp, and undamaged crystals with a distinct, prismatic habit. Luster and crystal size also play a significant role. Specimens with visible intergrowths with other rare minerals, such as euxenite, on a well-defined rock matrix (e.g., on quartz or feldspar) are more highly prized than isolated, rounded fragments. Due to metamictization, specimens that retain at least partially their original crystalline structure are rarer and more desirable. ## Popular Localities Classic and most famous specimens come from localities in Texas (USA), where the mineral was first described. High-quality crystals have also been found in pegmatites in Norway, in the Iveland region. Specimens from these historical localities are particularly sought after by collectors.

Care and storage

## Cleaning Yttrocrasite-(Y) specimens should generally not be wet cleaned. Any dirt, such as dust, is best removed with a soft brush or compressed air. Contact with water is not recommended. ## What to Avoid As a radioactive mineral, it requires special caution. Direct, prolonged skin contact should be avoided, and inhalation of dust that might be produced by crushing it should be absolutely avoided. It should not be heated or exposed to chemicals. Store away from radiation-sensitive materials. ## Storage Specimens should be stored in closed, lead-lined or thick-glass containers to minimize radiation emission. The container should be clearly labeled as radioactive material. It should be kept away from areas of permanent human habitation, especially bedrooms and living rooms. It should not be displayed in open showcases.

Sources

IMA Mineral List (CNMNC)