Kilchoanite
Chemical formula: Ca₆(SiO₄)(Si₃O₁₀)
Kilchoanite is a rare calcium silicate, forming colorless to white, fine crystals and aggregates, found in metamorphic limestones.
Properties
- Mohs hardness
- 5.5
- Color
- Colorless
- Luster
- Vitreous
- Streak
- White
- Density
- 2.992
- Cleavage
- Good on {100}, {010} and {001}
- Fracture
- Uneven
- Transparency
- Transparent,Translucent
- Crystal system
- Orthorhombic
Diagnostic features
## Identification Field identification of kilchoanite is practically impossible due to its occurrence as microscopic crystals. In a collection, it is identified based on the label and confirmed locality. Certain identification requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical microanalysis (EDS/WDS). ## Distinguishing from similar minerals It can be confused with other white, fine-grained calcium silicates, such as wollastonite, rankinite, or larnite, with which it often coexists. Distinguishing it from these is possible only through specialized laboratory tests. Visually, they are practically indistinguishable. ## Crystal forms Kilchoanite crystallizes as very small, platy or acicular crystals, often grouped into radial or tangled aggregates. Less commonly, it forms granular masses within the rock.
Geological environment
## Genesis Kilchoanite is a product of high-temperature contact metamorphism (pyrometamorphism) of carbonate rocks, such as limestones and marls. It forms in contact zones of these rocks with hot magmatic intrusions, most often of basic composition (e.g., gabbros, dolerites). It forms under conditions of high temperature and low pressure. ## Mineral associations This mineral often coexists with other calcium silicates formed under similar conditions. The most common associated minerals include: rankinite, larnite, spurrite, gehlenite, melilite, wollastonite, tilleyite, and calcite. ## Localities The most important and classic occurrences of kilchoanite are: - Kilchoan, Ardnamurchan, Scotland (type locality). - Scawt Hill, County Antrim, Northern Ireland. - Hatrurim Formation in Israel and the West Bank. - Kopeisk, Chelyabinsk Oblast, Russia. - Lakargi Mountain, North Caucasus, Russia. - Fuka, Okayama Prefecture, Japan.
Rarity
Very rare
For collectors
## Quality criteria The collector's appeal of kilchoanite specimens is very specific and primarily directed towards collectors of rare minerals and those specializing in "micromounts". The most highly valued specimens are those on which well-formed, though still microscopic, crystals are visible, preferably in association with other rare calcium silicates. Accurate documentation and confirmation of the locality are crucial, especially if it is the type locality (Kilchoan) or another classic occurrence. Purity and contrast with the rock matrix also increase the specimen's value.
Care and storage
## Cleaning Kilchoanite specimens should be cleaned very carefully, preferably using compressed air to remove dust. Due to its fragility and potential reactivity, avoid washing it in water, and especially avoid using any detergents or acids. If it is necessary to remove loose contaminants, a very soft brush can be used. ## What to avoid Absolutely avoid contact with acids, which can decompose it. The mineral is sensitive to shocks and impacts, which can lead to damage to delicate crystals. It should not be subjected to ultrasonic cleaning. Store away from moisture. ## Storage It is recommended to store kilchoanite specimens in closed, stable containers (e.g., "micromount" type) that protect against dust, moisture, and mechanical damage. Avoid exposure to direct sunlight, although there is no evidence of it fading.