Paulingite-Ca

Chemical formula: (Ca,K,Na,Ba,&#9744;)<sub>10</sub>(Si,Al)<sub>42</sub>O<sub>84</sub>·34H<sub>2</sub>O

Paulingite-Ca is a rare mineral from the zeolite group, forming characteristic spherical or isometric crystals with a vitreous luster.

## Characteristics Paulingite-Ca is a hydrated calcium, potassium, and sodium aluminosilicate, belonging to the zeolite group. It forms very characteristic, well-developed crystals, most often in the form of rhombic dodecahedra, which can reach up to 1 cm in diameter. These crystals are often transparent to translucent, with a vitreous luster. They usually occur as single, isolated crystals grown on the walls of rock fissures or within them. ## Physical Properties This mineral is characterized by a hardness of approximately 5 on the Mohs scale. Its crystals are brittle, and the fracture is uneven. The density of Paulingite-Ca is approximately 2.08-2.15 g/cm³. The luster is typically vitreous, and the streak is white. ## Colors and Varieties Paulingite-Ca is most often colorless, white, or less commonly yellowish. No named color or commercial varieties are distinguished. Variability in chemical composition (mainly the proportions of Ca, K, Na cations) leads to the existence of related minerals in the paulingite series, such as Paulingite-K. ## History and Name The mineral was first described in 1960 by W. B. Kamb and W. C. Oke. Its name honors Linus Pauling (1901-1994), an American chemist and crystallographer, Nobel laureate, for his fundamental contributions to the understanding of complex silicate structures. ## Uses Paulingite-Ca has no industrial applications. However, it is a mineral valued and sought after by collectors specializing in zeolites and micromounts due to its perfectly formed crystals.

Properties

Mohs hardness
5
Luster
Vitreous
Streak
White
Density
2.08-2.15
Cleavage
Imperfect on {110}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Cubic

Diagnostic features

## Identification The key diagnostic feature of paulingite is its characteristic, almost perfectly spherical or polyhedral crystals in the form of a rhombic dodecahedron. Occurrence in geodes and fissures in basaltic rocks is also a strong indicator. ## Distinguishing from Similar Minerals Paulingite-Ca can be confused with other zeolites forming isometric crystals, such as chabazite or analcime. However, chabazite often forms crystals with a shape similar to a cube (rhombohedra), and analcime forms icositetrahedra (trapezohedra). Accurate identification often requires analysis of crystal shape under magnification or instrumental methods. ## Crystal Forms Paulingite-Ca crystallizes in the isometric system, forming almost exclusively crystals in the form of a rhombic dodecahedron {110}. These crystals are usually isolated and grown on a substrate, rarely forming larger aggregates.

Geological environment

## Genesis Paulingite-Ca is a low-temperature hydrothermal mineral. It forms in vesicles and fissures in basic volcanic rocks, such as basalts. It crystallizes from aqueous solutions in the late stages of lava cooling. ## Mineral Associations It often co-occurs with other zeolites, such as phillipsite, herschelite (a variety of chabazite), chabazite, gismondine, garronite, as well as with calcite and various minerals from the smectite group (e.g., montmorillonite). ## Localities The most important and classic locality, from which the best specimens originate, is Riggins in Idaho County, USA. This mineral has also been found in basalts in Richmond (Victoria, Australia), in County Antrim in Northern Ireland, and in several localities in the Czech Republic (e.g., Vinarická Hora).

Rarity

Rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with sharp, well-formed, transparent, and lustrous crystals of the largest possible diameter. Attractive placement of crystals on a contrasting matrix and lack of damage are also important. Specimens from the classic Idaho locality are particularly sought after. ## Popular Localities By far the most known and valued specimens come from Three Mile Creek and Rock Creek near Riggins, Idaho County, USA. These localities have yielded the largest and best-formed paulingite crystals.

Care and storage

## Cleaning 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. Allow the specimen to dry completely at room temperature. ## What to Avoid As a zeolite, paulingite is sensitive to high temperatures, which can cause the loss of water from its structure and destruction of the crystal. Avoid contact with acids and other chemicals. Crystals are brittle and sensitive to impact and vibrations. ## Storage It is recommended to store specimens in closed, padded boxes (e.g., "micromount" type) to protect them from dust, mechanical damage, and sudden changes in humidity. Do not expose them to direct sunlight.

External references

Sources

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