Killalaite

Chemical formula: Ca₃.₂[H₀.₆Si₂O₇](OH)

Killalaite is a rare calcium silicate, forming colorless or white, fine crystals, found in metamorphosed limestones.

## Characteristics Killalaite is a mineral from the silicate group, chemically classified as a hydrated calcium silicate. It typically occurs as very small, lath-like or fibrous crystals, which rarely exceed 1 mm in length. It forms radial aggregates or tangled masses. It is colorless to white, with a white streak, and has a vitreous luster. Due to the small size of the crystals, its macroscopic features are difficult to observe without magnification. ## Physical Properties This mineral is characterized by a hardness of approximately 5 on the Mohs scale. It is transparent to translucent. Its density is about 2.93 g/cm³. It exhibits perfect cleavage in one direction. ## History and Name Killalaite was first described in 1974 by R. A. Exley, A. J. Eaton, G. L. Long, and C. M. B. Henderson. Its name comes from the town of Killala in County Mayo, Ireland, near which its type locality, Inishcrone (Enniscrone), is located.

Properties

Mohs hardness: 5
Luster: Vitreous
Streak: White
Density: 2.93
Cleavage: Perfect on {100}
Fracture: Uneven
Transparency: Transparent to translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Field identification of killalaite is practically impossible due to its occurrence as microscopic crystals. It requires advanced laboratory methods, such as X-ray diffraction (XRD) or chemical analysis (EDS/WDS). Visually, it can be suspected in an appropriate geological environment when it forms white, fibrous coatings or radial aggregates on the host rock. ## Distinguishing from similar minerals It can be confused with other white, fibrous calcium silicates, such as afwillite, okenite, or tobermorite. Definitive differentiation is only possible based on structural and chemical analysis. ## Crystal forms It forms elongated, lath-like crystals, often flattened. They usually occur as radial or tangled aggregates, as well as fine veins cutting through the rock.

Geological environment

## Genesis Killalaite is a product of contact metamorphism. It forms in contact zones of basic intrusions (e.g., dolerites) with Cretaceous limestones or other calcium carbonate-rich rocks. High temperature and chemical reactions between the magma and the sedimentary rock lead to the formation of specific minerals, including killalaite. ## Mineral associations This mineral co-occurs with other products of contact metamorphism, such as larnite, spurrite, gehlenite, rankinite, afwillite, and calcite. ## Localities The most important and classic locality, which is also the type locality, is Inishcrone (Enniscrone) in Ireland. This mineral has also been confirmed in Carneal in Northern Ireland and in several locations in Israel, in the Hatrurim Formation in the Negev Desert.

Rarity

Very rare

For collectors

## Quality criteria As a "micromount" type mineral, the value of killalaite is primarily determined by the quality and abundance of crystals on the rock matrix. Specimens with well-formed, radial aggregates that are clearly visible under a microscope are most prized. Association with other rare contact metamorphic minerals is also important.

Care and storage

## Cleaning Due to the fragility and small size of the crystals, mechanical cleaning is not recommended. If necessary, compressed air can be used to remove dust. Contact with water, especially acids, can be risky. ## What to avoid Contact with acids, which can damage the mineral, should be avoided. Specimens should be protected from shocks and impacts that could destroy the delicate crystals. ## Storage Killalaite specimens are best stored in enclosed "micromount" boxes, which protect them from dust and mechanical damage. Due to its rarity and delicacy, it is not suitable for display outside such protection.

Sources

IMA Mineral List (CNMNC)