Chlormayenite
Chemical formula: Ca<sub>12</sub>Al<sub>14</sub>O<sub>32</sub>[☐<sub>4</sub>Cl<sub>2</sub>]
Chlormayenite is a rare mineral from the mayenite group, occurring as microscopic, colorless or white grains in skarns and limestone xenoliths.
Properties
- Mohs hardness
- 5.5
- Luster
- Vitreous
- Streak
- White
- Density
- 2.75
- Cleavage
- None
- Fracture
- Conchoidal
- Transparency
- Transparent to Translucent
- Crystal system
- Cubic
Diagnostic features
## Identification Identification of chlormayenite is impossible without advanced analytical techniques. It requires the use of a scanning electron microscope (SEM) with chemical composition analysis (EDS) or X-ray diffraction (XRD). In collector's conditions, recognition relies on identifying the host rock and associated minerals, typical of its occurrence environment. ## Distinguishing from Similar Minerals It can be confused with other minerals from the mayenite group, such as fluormayenite, which have identical appearance and physical properties. Differentiation is possible only based on chemical analysis showing the dominance of chlorine over fluorine. From other colorless, microscopic minerals (e.g., quartz, calcite), it is distinguished by its occurrence environment and chemical composition. ## Crystal Forms It forms very small, isometric (regular) crystals, often dodecahedral or icositetrahedral in shape, although it is usually observed as rounded, amorphous grains and aggregates.
Geological environment
## Genesis Chlormayenite forms under conditions of high-temperature, low-pressure contact metamorphism. It develops in skarns formed at the contact of magmatic intrusions with carbonate sedimentary rocks (limestones, dolomites) and in limestone xenoliths entrained by lava. ## Mineral Associations It often co-occurs with minerals such as larnite, shulamitite, gehlenite, brownmillerite, spinel, perovskite, grossular, diopside, and calcite. ## Localities Key localities for this mineral worldwide include the Hatrurim Formation in Israel (type locality), the Bellerberg volcano region in the Eifel Mountains in Germany, and some localities in Russia (e.g., in the Chelyabinsk Oblast).
Rarity
Very rare
For collectors
## Quality Criteria From a collector's perspective, the value of a chlormayenite specimen does not depend on the mineral itself, which is invisible to the naked eye. Instead, the richness and aesthetics of the entire assemblage of associated minerals from a classic, rare locality are important. A specimen is valued if it contains well-identified, rich concentrations of chlormayenite confirmed by analysis, in association with other rare skarn minerals. ## Popular Localities The most known and prized specimens by collectors come from the Eifel volcanic complex in Germany, where chlormayenite occurs in altered limestone xenoliths. Specimens from the Hatrurim Formation in Israel are primarily of scientific importance.
Care and storage
## Cleaning Specimens containing chlormayenite, due to its microscopic nature, should be cleaned with the utmost care. The safest method is to use compressed air to remove dust. Avoid washing with water, which may react with the mineral or associated minerals. ## What to Avoid Avoid contact with acids and other chemicals that can damage both chlormayenite and the host rock. The mineral is sensitive to moisture and can undergo alterations upon contact with water. ## Storage Samples should be stored in a dry place, preferably in tightly sealed containers or display cases, to protect them from moisture and contaminants. Due to the microscopic nature of the crystals, specimens do not require special protection from light or mechanical damage, but protecting the host rock is crucial.