Neighborite

Chemical formula: NaMgF<sub>3</sub>

Neighborite is a rare sodium magnesium fluoride, forming colorless or white, pseudocubic crystals with a vitreous luster.

## Characteristics Neighborite is a sodium magnesium fluoride with a perovskite structure. It occurs as small, usually anhedral (irregular) grains or as well-formed, though small, pseudocubic crystals. Its appearance is inconspicuous – it is most often colorless or white, which, combined with the small size of the crystals, makes it easy to overlook. Crystals can be transparent and exhibit a vitreous luster. ## Physical Properties This mineral is characterized by a hardness of 4.5 on the Mohs scale, placing it in the medium hardness range. It has a relatively low density, approximately 3.03 g/cm³. It is transparent to translucent, and its luster is described as vitreous. ## Colors and Varieties Neighborite is typically colorless or white. Some specimens may show a pale gray tint. No named varieties of this mineral are distinguished. ## History and Name Neighborite was discovered in drill core samples from the Green River Formation in Uintah County, Utah, USA. It was described in 1961 by E. C. T. Chao, H. T. Evans, Jr., B. J. Skinner, and C. Milton. The mineral is named in honor of Frank Neighbor, a consulting geologist for Sun Oil Company, who first drew attention to unusual minerals in drill cores from this area, leading to the discovery of neighborite and other new mineral species. ## Uses Neighborite has no industrial application. Its significance is purely scientific and as a collector's item, as a rare fluoride mineral and a member of the perovskite group.

Properties

Mohs hardness
4.5
Luster
Vitreous
Streak
White
Density
3.03
Cleavage
Perfect on {110}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Neighborite is difficult to identify visually without knowledge of the geological context. Key features include its pseudocubic crystal habit, vitreous luster, hardness of approximately 4.5, and occurrence in a specific evaporitic environment. It reacts with sulfuric acid. Identification usually requires advanced analytical methods, such as X-ray diffraction (XRD). ## Distinguishing from Similar Minerals It can be confused with other colorless or white minerals with a vitreous luster, such as halite, cryolite, or some feldspars. It differs from halite by its significantly greater hardness and lack of a salty taste. It differs from cryolite by its higher hardness and different optical properties. In its occurrence, it is sometimes confused with other rare salt minerals. ## Crystal Forms Neighborite crystals, although belonging to the orthorhombic system, exhibit a strongly pseudocubic appearance. They often form simple cubes or complex forms resembling isometric crystals. They occur as single, overgrown crystals or as granular aggregates within the host rock.

Geological environment

## Genesis Neighborite is an authigenic mineral, crystallizing under specific geochemical conditions. It forms in sediments rich in sodium, magnesium, and fluorine, in an evaporitic environment with high salinity and alkalinity. Its typical formation site is in carbonate- and organic-rich shales and siltstones of the Green River Formation. ## Mineral Associations This mineral co-occurs with a number of other rare evaporite minerals. In the type locality (Green River Formation), its associated minerals include nahcolite, shortite, trona, halite, as well as newly discovered minerals such as garrelsite, burbankite, loughlinite, and reedmergnerite. ## Localities The most important and classic locality for neighborite is the Green River Formation in Utah and Colorado, USA, where it was discovered. It is also known from alkaline intrusions on the Kola Peninsula in Russia (Khibiny and Lovozero massifs) and from the Ilimaussaq igneous complex in Greenland. These are the only confirmed and well-documented occurrences of this mineral.

Rarity

Very rare

For collectors

## Quality Criteria The most prized specimens by collectors are those with sharp, well-formed, pseudocubic crystals, clearly distinct from the host rock. Transparency and lack of damage are highly valued. Due to the small size of the crystals (usually a few millimeters), even small but well-formed specimens are sought after. Contrast with a darker matrix enhances visual appeal. ## Popular Localities By far, the most desirable specimens come from the classic locality in the Green River Formation in Uintah County, Utah, USA. Specimens from the Kola Peninsula or Greenland, while scientifically important, less frequently form aesthetic crystals and are mainly of interest to collectors specializing in mineral systematics (so-called "systematists").

Care and storage

## Cleaning Neighborite specimens should be cleaned very carefully. It is best to use a soft brush to remove dust. If wet cleaning is necessary, use distilled water and avoid prolonged soaking. After cleaning, the specimen should be thoroughly dried. ## What to Avoid Neighborite is sensitive to acids, which can damage it. Contact with household and laboratory chemicals should be avoided. It should not be subjected to ultrasonic cleaning or steam cleaning. Due to its moderate hardness, it should be protected from scratching by harder minerals (e.g., quartz). ## Storage Neighborite specimens, especially those with well-formed crystals, should be stored in separate, padded boxes to prevent abrasion and mechanical damage. It is stable under household conditions and does not require special protection from light or humidity, but extreme conditions should be avoided.

External references

Sources

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