Norsethite

Chemical formula: BaMg(CO<sub>₃</sub>)<sub>₂</sub>

A rare barium and magnesium carbonate from the dolomite group, forming characteristic, vitreous rhombohedral crystals.

## Characteristics Norsethite is a rare mineral from the dolomite group, being a double carbonate of barium and magnesium. It most often forms well-developed, lustrous rhombohedral crystals, whose faces can sometimes be curved or stepped. It also occurs in granular and massive aggregates. It is a mineral valued by collectors due to its rarity and classic crystalline form. ## Physical Properties Norsethite has a hardness of 3.5 on the Mohs scale, making it a relatively soft mineral. It has a vitreous luster and is transparent to translucent. Its density is relatively high for a carbonate, approximately 3.84 g/cm³, which is a diagnostic feature related to the presence of heavy barium in the structure. It possesses perfect, three-directional rhombohedral cleavage. ## Colors and Varieties This mineral is most often colorless or white. It can also be colored in shades of gray, pale yellow, or brownish, usually due to impurities or inclusions. No commercial or colored varieties are distinguished. ## History and Name Norsethite was first described in 1959 by a team of mineralogists (M. E. Mrose, E. C. T. Chao, J. J. Fahey, C. L. Christ). Its name honors Keith Norseth, a geologist who discovered this mineral in the Westvaco mine in Sweetwater County, Wyoming, USA. This locality, located within the Green River Formation, remains the type locality for this mineral. ## Uses Due to its rarity and small accumulations, norsethite has no industrial application. It is solely an object of scientific and collecting interest.

Properties

Mohs hardness: 3.5
Luster: Vitreous
Streak: White
Density: 3.83 - 3.84
Cleavage: Perfect on {1011}
Fracture: Conchoidal to uneven
Transparency: Transparent to translucent
Crystal system: Trigonal

Diagnostic features

## Identification Key diagnostic features of norsethite include its high density (approx. 3.84 g/cm³), unusual for most carbonates with a vitreous luster. Perfect rhombohedral cleavage, relatively low hardness (3.5), and crystal form are also helpful in identification. It reacts with hydrochloric acid, but more slowly than calcite. ## Distinguishing from Similar Minerals Norsethite can be confused with other carbonates such as calcite, dolomite, or ankerite. It is distinguished from them by its significantly higher density. From calcite, it differs by a slower reaction with acid. From barytocalcite (BaCa(CO₃)₂) and witherite (BaCO₃), it can be difficult to distinguish without advanced studies (XRD, EDS), but crystal form and occurrence environment (mineral associations) are often sufficient clues. ## Crystal Forms Norsethite crystallizes in the trigonal system, forming rhombohedral crystals. These are often simple rhombohedra, but complex forms with curved or stepped faces are also found. It also occurs in granular aggregates.

Geological environment

## Genesis Norsethite is a sedimentary mineral, forming under highly alkaline and saline conditions in evaporitic lakes. It is an authigenic mineral, crystallizing directly from waters rich in barium, magnesium, and carbonate ions. The classic environment for its formation is the shales and mudstones of the Green River Formation in the USA. ## Mineral Associations This mineral often co-occurs with other rare evaporitic minerals characteristic of its type locality. These include shortite, eitelite, loughlinite, searlesite, pirssonite, as well as more common minerals such as dolomite, calcite, and trona. ## Localities The most important and well-known worldwide locality for norsethite is the Green River Formation in Sweetwater County, Wyoming (USA), especially the area of the Westvaco mine. Specimens from this locality are the type material for the species. Other, much rarer occurrences have been reported, among others, in alkaline rocks on the Kola Peninsula in Russia.

Rarity

Rare

For collectors

## Quality Criteria The most highly valued norsethite specimens are those consisting of sharp, well-formed, transparent, and colorless crystals with a strong luster. The size of the crystals and the absence of mechanical damage, especially along cleavage planes, are of great importance. The aesthetic placement of the specimen on a rock matrix or its co-occurrence with other rare minerals, such as shortite or eitelite, also enhances its attractiveness. ## Popular Localities By far the most sought-after specimens by collectors come from the classic locality in the Green River Formation in Wyoming, USA. This locality has provided the world's best crystals of this mineral and is considered the only source of commercially significant specimens.

Care and storage

## Cleaning Norsethite specimens should be cleaned very carefully, using a soft brush to remove dust. It can be rinsed with distilled water, but prolonged soaking should be avoided. Ultrasonic cleaners are not recommended, as they can damage the specimen along cleavage planes. ## What to Avoid As a carbonate, norsethite is sensitive to acids, even weak ones – they cause its rapid dissolution. It should be protected from contact with household chemicals. It is a soft mineral, susceptible to scratching by harder minerals (e.g., quartz), and therefore requires careful handling. ## Storage It is recommended to store specimens in separate, padded boxes or display cases to avoid scratches and impacts. It does not require special conditions regarding humidity or lighting, but exposure to direct sunlight, which can affect some specimens over time, should be avoided.

Sources

IMA Mineral List (CNMNC)