Okanoganite-(Y)

Chemical formula: (Y,REE,Ca,Na,Th₄+)₁₆(Fe₃+,Ti₄+)(Si,B,P)₁₀(O,OH)₃₈F₁₀

Okanoganite-(Y) is an extremely rare borosilicate of yttrium and rare earth metals, forming characteristic, radial aggregates of a creamy or yellowish color.

## Characteristics Okanoganite-(Y) is a complex borosilicate containing yttrium, rare earth elements, sodium, and fluorine. This mineral almost always occurs in the form of spherulitic or radial aggregates, which consist of very fine, acicular or fibrous crystals. Individual crystals are rarely visible to the naked eye. These aggregates typically range from a few millimeters to about a centimeter in diameter and exhibit a delicate, fibrous structure on the fracture surface. ## Physical Properties Its Mohs hardness is approximately 4.5, making it a relatively soft mineral. The luster is described as vitreous on crystal faces (though rarely observed) and silky or dull on aggregate surfaces. It is a translucent to opaque mineral. The density is approximately 3.36 g/cm³. ## Colors and Varieties Okanoganite-(Y) occurs in a limited range of colors, most commonly from creamy white, through pale yellow, to yellowish-brown. No color or commercial varieties are distinguished. ## History and Name The mineral was first described in 1980. Its name comes from the discovery locality - Okanogan County in Washington State, USA. The "-(Y)" suffix in the name (a so-called Levinson modifier) indicates that yttrium (Y) is the dominant rare earth element in its chemical structure. ## Applications Due to its extreme rarity, okanoganite-(Y) has no industrial applications. It is solely an object of scientific interest and is a highly valued specimen in advanced collections of rare and systematic minerals. The presence of thorium in its structure means it can exhibit weak radioactivity.

Properties

Mohs hardness: 4.5
Luster: Vitreous to Silky
Streak: White to pale yellow
Density: 3.36
Cleavage: Good on {0001}
Fracture: Uneven
Transparency: Translucent to Opaque
Crystal system: Trigonal

Diagnostic features

## Identification The most important diagnostic feature of okanoganite-(Y) is its mode of occurrence - radial, spherical aggregates with a fibrous structure. Its characteristic color (creamy to yellowish) and specific geological environment are also distinctive. ## Distinguishing from Similar Minerals It can be confused with other rare earth minerals of similar habit, such as some zeolites, kainosite-(Y), or rare micas. However, many of these minerals have different hardness or color. Definitive and certain distinction from similar minerals, especially from other REE borosilicates, requires advanced analytical methods such as X-ray diffraction (XRD) or chemical microanalysis (EDS/WDS). ## Crystal Forms Okanoganite-(Y) crystals are trigonal, but almost never occur as well-formed, single individuals. It forms almost exclusively spherulitic (spherical) and radial aggregates, composed of tightly packed, very fine fibers or needles.

Geological environment

## Genesis Okanoganite-(Y) is a pneumatolytic or hydrothermal mineral. It forms in the late stages of crystallization of granite pegmatites, rich in alkaline and rare earth elements. It occurs in vugs (miaroles) within these pegmatites. ## Mineral Associations This mineral co-occurs with other rare pegmatite minerals. Its typical associations include zektzerite, aegirine, astrophyllite, zircon, allanite-(Ce), and gadolinite-(Y). ## Localities The most important and classic locality, from which the best specimens originate, is its type locality - Washington Pass in Okanogan County, Washington State, USA. This is one of only a few confirmed occurrences of this mineral in the world.

Rarity

Extremely rare

For collectors

## Quality Criteria The most highly valued okanoganite-(Y) specimens are those that exhibit well-formed, complete spherulites with an intense, yellowish color. Aggregates embedded on a contrasting rock matrix or co-occurring with other rare minerals, such as zektzerite, are particularly desirable. The size of the aggregates and their abundance on the specimen also significantly increase its collector's value. ## Popular Localities The vast majority, if not all, specimens available on the collector's market come from a single location - the pegmatites in the Washington Pass area of Washington State, USA. Specimens from any other locality would be a collector's sensation.

Care and storage

## Cleaning Okanoganite-(Y) specimens should only be cleaned mechanically, using a soft brush to remove dust. Due to the fibrous structure of the aggregates, washing in water is not recommended, as moisture can be difficult to remove from between the fibers. Absolutely avoid ultrasonic cleaners and all chemical agents. ## What to Avoid The mineral is sensitive to acids. Contact with chemicals should be avoided. Due to possible, though usually low, radioactivity (associated with the presence of thorium), caution is advised when handling the mineral - avoid inhaling dust and wash hands after contact. ## Storage It is recommended to store specimens in closed, stable containers (e.g., "perky boxes") to protect delicate, fibrous aggregates from mechanical damage and dust. Radioactive specimens should be stored away from light-sensitive materials and other minerals whose color may change due to radiation (e.g., smoky quartz, fluorite).

Sources

IMA Mineral List (CNMNC)