Sanbornite

Chemical formula: BaSi<sub>2</sub>O<sub>5</sub>

Sanbornite is a rare barium silicate, forming colorless or white, tabular crystals with a pearly luster.

## Characteristics Sanbornite is a rare mineral from the phyllosilicate group, chemically a barium silicate. It occurs as tabular, lath-like, or platy crystals, often forming rosette-like or fan-shaped aggregates. Specimens are usually small, and well-formed crystals are rare. It is typically colorless to white, sometimes with a pale pink hue. ## Physical Properties This mineral is characterized by a hardness of 5 on the Mohs scale and a density of approximately 3.7 g/cm³. It possesses perfect cleavage in one direction, making it easily separable into thin lamellae. The luster on cleavage surfaces is pearly, while on other surfaces it is vitreous. ## Colors and Varieties Sanbornite is usually colorless or white. Some specimens may exhibit a pale pink or greenish tint, which is likely due to trace impurities. No named varieties of this mineral are recognized. ## History and Name Sanbornite was first described in 1932. Its name comes from Frank Sanborn (1862-1936), a mineralogist from the California Department of Natural Resources, who first identified it as a new mineral. The type locality is the Incline area in Mariposa County, California, USA. ## Uses Due to its rarity, sanbornite has no industrial applications. It is sought after and valued exclusively by mineral collectors and scientific institutions.

Properties

Mohs hardness
5
Luster
Pearly, Vitreous
Streak
White
Density
3.7 - 3.76
Cleavage
Perfect on {001}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Key diagnostic features of sanbornite include its tabular habit, perfect cleavage in one direction, pearly luster on cleavage planes, and relatively high density for a silicate. It often occurs in characteristic, rosette-like aggregates. ## Distinguishing from Similar Minerals Sanbornite can be confused with other white, platy minerals, such as micas (e.g., muscovite) or talc. However, it is distinguished by its higher hardness (5 on the Mohs scale) and significantly greater density. Unlike micas, its lamellae are not elastic. ## Crystal Forms Crystals are tabular or lath-like, often with a pseudohexagonal outline. It forms rosette-like, fan-shaped, platy, or granular aggregates.

Geological environment

## Genesis Sanbornite is a metamorphic mineral. It forms as a result of contact metamorphism in barium-rich rocks, such as barite deposits, or in barium-bearing gneisses and quartzites. It forms under conditions of relatively high temperature and low to medium pressure. ## Mineral Associations This mineral often co-occurs with quartz, gillespite, celsian, diopside, tridymite, titanite, tourmaline, and various garnets. ## Localities The most important and classic localities for sanbornite are in California, USA, especially Rush Creek (Fresno County) and the Incline area (Mariposa County), where it was discovered. It also occurs in Big Creek (Fresno County). Outside the USA, its presence has been noted in the Tanohata mine in Japan and the Trumbull Peak deposit in British Columbia, Canada.

Rarity

Rare

For collectors

## Quality Criteria The most desirable specimens for collectors are those with well-formed, sharp crystals forming aesthetic, rosette-like or fan-shaped aggregates. Specimens where sanbornite contrasts with colorful associated minerals, such as red gillespite, are also highly valued. Crystal size and lack of damage significantly increase the value of a specimen. ## Popular Localities By far the most prized and classic specimens come from localities in California, USA, especially Rush Creek and Big Creek in Fresno County. Specimens from these locations, often with associated gillespite, are considered the standard for this species.

Care and storage

## Cleaning Sanbornite specimens should be cleaned very carefully, using a soft brush to remove dust. Due to its perfect cleavage, it is very brittle and prone to delamination. Avoid ultrasonic cleaners and strong streams of water. ## What to Avoid Avoid contact with acids and other aggressive chemicals. The mineral is susceptible to mechanical damage, so it should be protected from impacts, falls, and scratching by harder minerals. ## Storage It is recommended to store specimens in separate, padded boxes to prevent contact with other minerals. It should be protected from dust and mechanical damage.

External references

Sources

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