Stokesite

Chemical formula: CaSn⁴⁺Si₃O₉·2H₂O

Stokesite is a rare calcium tin silicate, forming colorless or white crystals, prized by collectors specializing in tin minerals.

## Characteristics Stokesite is a hydrated calcium tin silicate, belonging to the group of rare minerals. It occurs in the form of well-developed, prismatic or tabular crystals, often gathered in radial or fan-shaped aggregates. Specimens are usually small, and individual crystals rarely exceed a few millimeters in length. The mineral is transparent to translucent and characterized by a vitreous luster. ## Physical Properties Stokesite has a hardness of 6 on the Mohs scale, making it a relatively scratch-resistant mineral. Its density is approximately 3.185 g/cm³, making it noticeably heavier than most common silicates. It exhibits perfect cleavage in one plane and imperfect cleavage in another, and its fracture is conchoidal. ## Colors and Varieties This mineral is most often colorless or white. Rarer specimens have a delicate, pale blue tint. There are no named color varieties or commercial varieties. ## History and Name Stokesite was first described in 1899. Its name commemorates Sir George Gabriel Stokes (1819-1903), an Irish mathematician and physicist, professor at Cambridge University, who made significant contributions in the field of optics and mineral fluorescence. ## Uses Due to its rarity and small crystal size, stokesite has no industrial applications. It is solely a mineral of scientific and collector's interest.

Properties

Mohs hardness
6
Luster
Vitreous
Streak
White
Density
3.185
Cleavage
Perfect on {101} imperfect on {100}
Fracture
Conchoidal
Transparency
Transparent,Translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Stokesite can be identified by its characteristic crystal shape, often forming radial aggregates. Its vitreous luster, hardness (6 on the Mohs scale), and relatively high density are helpful in identification. Its occurrence in association with other tin minerals, such as cassiterite, is a strong diagnostic indicator. ## Distinguishing from Similar Minerals Stokesite is sometimes confused with some zeolites (e.g., natrolite) due to similar, radial aggregate forms. However, it is distinguished by its higher hardness and density. It can also be confused with quartz, from which it differs in crystal form and perfect cleavage (quartz does not possess it). ## Crystal Forms Stokesite crystals are columnar or tabular, often elongated and terminated by steep pyramids. They usually occur as radial or fan-shaped aggregates, growing from a common center. Single, well-formed crystals are rarer.

Geological environment

## Genesis Stokesite is a mineral of hydrothermal origin. It forms in the late stages of crystallization within gas cavities (geodes) and fissures in basic rocks, such as diabases, and in pegmatite veins and skarns associated with granitic intrusions. ## Mineral Associations This mineral often co-occurs with other tin minerals and silicates. The most common associations include: cassiterite, axinite, datolite, epidote, quartz, calcite, and zeolites. ## Localities The most important and classic locality for stokesite is its type locality in Cornwall, England (Stamps and Jowl Zawn, Botallack, St Just). It is also known from several other places in the world, including Russia (Urals), Italy (Elba Island), and the United States (California).

Rarity

Very rare

For collectors

## Quality Criteria The most prized stokesite specimens are those with sharp, well-formed, and transparent crystals, forming aesthetic, radial aggregates. Crystal size is important – specimens with needles exceeding a centimeter are rare. A contrasting matrix, for example with dark cassiterite, significantly enhances the visual appeal and value of the specimen. ## Popular Localities By far the most sought-after by collectors are classic specimens from the historical localities in Cornwall, England. These are considered exemplary for the species and command the highest prices in the collector's market.

Care and storage

## Cleaning Stokesite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, distilled water can be used, but prolonged soaking should be avoided. Mechanical cleaning should be performed without the use of strong chemical agents. ## What to Avoid The mineral is sensitive to acids and strong bases. Avoid sudden temperature changes and ultrasonic cleaners, which could damage crystals along cleavage planes. ## Storage Stokesite should be stored in separate, padded boxes to prevent scratching by harder minerals. Due to its perfect cleavage, it is sensitive to impacts and pressure. It is best displayed in closed display cases, protected from dust and mechanical damage.

External references

Sources

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