Barnesite
Chemical formula: Na<sub>2</sub>V<sup>5+</sup><sub>6</sub>O<sub>16</sub>·3H<sub>2</sub>O
Barnesite is a hydrated sodium vanadate, forming characteristic fibrous aggregates of a reddish-brown color.
Description
## Characteristics Barnesite is a mineral from the vanadate group, chemically classified as a hydrated sodium vanadate. It occurs as aggregates of small, platy or fibrous crystals, which often arrange into radial aggregates or form felted, matted masses. Its most characteristic visual feature is an intense, reddish-brown to dark red color. ## Physical Properties This mineral is characterized by a hardness of approximately 3 on the Mohs scale, making it relatively soft. The luster of barnesite is most often silky, which is typical for minerals with a fibrous structure; it can also be described as dull or subadamantine. It is translucent, and its density is approximately 3.16 g/cm³. ## Colors and Varieties Barnesite occurs in a uniform range of colors, from reddish-brown to dark red. No commercial names or color varieties are distinguished for it. Its color is directly related to the presence of vanadium in its structure. ## History and Name The mineral was first described in 1963. Its name honors William H. Barnes (1903–1989), a Canadian physicist and crystallographer from the National Research Council in Ottawa, who made significant contributions to the study of vanadium minerals. ## Applications Due to its rarity and occurrence in small quantities, barnesite has no industrial application. It is solely an object of scientific interest and is valued by specialized mineral collectors.
Diagnostic features
## Identification Key features for identifying barnesite are its reddish-brown color, silky luster, and characteristic form as fibrous or felted aggregates. Its occurrence environment – oxidation zones of uranium-vanadium deposits in sandstones – is also an important indicator. ## Distinguishing from Similar Minerals Barnesite can be confused with other secondary vanadium minerals of similar appearance, such as hewettite (CaV₆O₁₆·9H₂O) or metahewettite. Hewettite has a very similar habit and color but is a calcium vanadate, not a sodium vanadate. Final distinction of these minerals often requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical analysis. ## Crystal Forms It forms elongated, platy crystals, which usually occur as dense, radial, or tangled fibrous aggregates. Single, well-formed crystals are rarely observed.
Geological environment
## Genesis Barnesite is a secondary mineral, formed in the oxidation zones of uranium-vanadium deposits, which are located in sedimentary rocks, mainly sandstones. It forms as a result of weathering and alteration of primary vanadium minerals, such as montroseite or corvusite, under low temperature and pressure conditions. ## Mineral Associations It most commonly co-occurs with other secondary vanadium minerals, such as hewettite, metahewettite, tyuyamunite, carnotite, as well as with primary ore minerals like montroseite and corvusite. It is also accompanied by gypsum, barite, and clay minerals. ## Localities The most important and classic barnesite localities are on the Colorado Plateau in the USA, especially in Utah (e.g., Cactus Rat mine in Grand County - type locality), Colorado, and Arizona. This is the main region of occurrence for this mineral worldwide.
Rarity
Rare
Collector aspects
## Quality Criteria The most valued by collectors are specimens with rich, well-formed, radial aggregates of fibrous crystals of intense, reddish-brown color. A clear contrast with the light matrix rock (sandstone) enhances its attractiveness. The size and lack of damage to the delicate aggregates are also important. ## Popular Localities Specimens of the highest collectible value come from historical localities on the Colorado Plateau in the USA. Mines in the Thompson area of Grand County, Utah, have provided many classic samples of this mineral.
Care and storage
## Cleaning Barnesite specimens are delicate and relatively soft. For dust removal, it is best to use a soft brush or compressed air from a safe distance. Wet cleaning should be avoided, as the mineral may be partially soluble in water. ## What to Avoid Contact with water, acids, and other chemicals must be strictly avoided. The mineral is sensitive to moisture and can dehydrate under heat. Its fibrous aggregates are brittle and susceptible to mechanical damage, thus requiring careful handling. ## Storage It is recommended to store specimens in a dry place, in sealed containers (e.g., "perky box" type), which protect delicate fibers from damage, dust, and changes in humidity. Exposure to direct sunlight and sudden temperature changes should be avoided.