Ye'elimite

Chemical formula: Ca₄Al₆O₁₂S⁶⁺O₄

Ye'elimite is a rare calcium sulfoaluminate, occurring as colorless, isometric crystals, a key component of Portland cement.

## Characteristics Ye'elimite is a rare sulfate mineral, chemically defined as calcium sulfoaluminate. It most commonly occurs as very fine, isometric (cubic) crystals, which rarely reach sizes visible to the naked eye. It usually forms granular aggregates or occurs as inclusions in other minerals. It is colorless and translucent. ## Physical Properties Ye'elimite crystals exhibit a vitreous luster. Due to the extremely small size of natural crystals, many of its physical properties, such as hardness or density, have not been precisely determined for natural material. However, it is an important synthetic component in the cement industry. ## Colors and Varieties This mineral is typically colorless. No colored or commercial varieties are distinguished. ## History and Name The mineral's name comes from its discovery locality – Mount Har Ye'elim in the Hatrurim Basin, Israel, where it was first identified in 1984 by Shulamit Gross. The name directly refers to the type locality. ## Applications Natural ye'elimite is solely an object of scientific and collecting interest. Its synthetic counterpart, known as "Klein's phase" or C₄A₃S̅ in cement notation, is a key component of some specialized cements, e.g., calcium sulfoaluminate (CSA) cements, valued for their rapid strength gain and low CO₂ emissions during production.

Properties

Luster: Vitreous
Density: 0
Transparency: Translucent
Crystal system: Isometric

Diagnostic features

## Identification Identification of ye'elimite under amateur conditions is practically impossible due to the microscopic size of its crystals. It requires advanced analytical methods, such as X-ray diffraction (XRD) or chemical microanalysis (EDS/WDS). Its occurrence in the specific geological environment of the Hatrurim Formation is a key indicator. ## Distinguishing from similar minerals It can be confused with other colorless, fine-grained minerals found in the same environment, such as larnite or brownmillerite. Definitive differentiation is only possible using specialized laboratory techniques. ## Crystal forms It forms very small, isometric (cubic) crystals, often tetrahedral in habit or as rounded grains. It usually occurs as fine-grained aggregates within the host rock.

Geological environment

## Genesis Ye'elimite is a metamorphic mineral formed under pyrometamorphic conditions – the natural, high-temperature burning of sedimentary rocks (marls, limestones). This process occurs due to the combustion of underground bituminous deposits, leading to the formation of a unique mineral assemblage within the so-called Hatrurim Formation. ## Mineral associations This mineral co-occurs with other rare minerals formed under pyrometamorphic conditions, such as larnite, brownmillerite, spurrite, mayenite, as well as gypsum and anhydrite. ## Localities The most important and classic locality for ye'elimite is the Hatrurim Formation, extending across Israel and Palestine. Its presence has been confirmed, among others, on Mount Har Ye'elim (type locality), in the Ma'ale Adummim area, and in Nabi Musa. Outside this region, its occurrence is extremely rare.

Rarity

Very rare

For collectors

## Quality criteria Due to the microscopic nature of the mineral, its collector value is mainly related to the abundance of its occurrence in the host rock and its scientifically confirmed identity. Specimens where ye'elimite forms slightly larger aggregates visible under a magnifying glass are more valued. The precise locality of the specimen's origin is crucial. ## Popular localities The only source of collector specimens is the Hatrurim Formation in Israel. Specimens from the type locality, Har Ye'elim, are most sought after by specialized collectors of rare minerals.

Care and storage

## Cleaning Ye'elimite specimens, due to their small size and occurrence within the host rock, generally do not require cleaning. If necessary, use only a soft brush to remove dust. ## What to avoid Avoid contact with water and chemicals, especially acids, which can damage the mineral and the surrounding rock. Do not subject it to ultrasonic cleaning or sudden temperature changes. ## Storage Specimens should be stored in stable conditions, in a dry place, away from direct sunlight. It is best to keep them in sealed collector boxes to protect them from dust and mechanical damage.