Emeleusite

Chemical formula: Na₂LiFe₃+Si₆O₁₅

A very rare sodium, lithium, and iron silicate, forming pale, acicular crystals in alkaline pegmatites.

## Characteristics Emeleusite is a rare silicate mineral belonging to the rare tuite group. It typically forms small, prismatic or acicular crystals, often gathered in radial aggregates. Its appearance is subtle, with dominant pale hues and a vitreous luster. It is transparent to translucent. Due to its occurrence in specific geological environments, it is a mineral valued by specialized collectors. ## Physical Properties This mineral is characterized by a Mohs hardness in the range of 5-6, making it relatively scratch-resistant. It has a density of approximately 2.77 g/cm³. It possesses good, bidirectional cleavage, which can be seen as stepped fractures on the crystal surfaces. The luster is typically vitreous. ## Colors and Varieties Emeleusite is most often pale pink, but colorless or grayish specimens are also found. The intensity of the color is usually weak. No named color varieties or commercial varieties are distinguished. ## History and Name The mineral was discovered and described in 1977. Its name comes from Charles Henry Emeleus (1930–2017), a professor of petrology at Durham University in England. He was honored for his contributions to the study of the petrology of the Gardar Province in southern Greenland, where the type locality of this mineral is found (Ilimaussaq alkaline complex). ## Uses Emeleusite has no industrial application. Its significance is purely scientific and collectible.

Properties

Mohs hardness: 5-6
Luster: Vitreous
Streak: White
Density: 2.77
Cleavage: Good on {110} and {010}
Fracture: Uneven
Transparency: Transparent to Translucent
Crystal system: Orthorhombic

Diagnostic features

## Identification Helpful features for identifying emeleusite include its pale pink color, vitreous luster, and crystal habit – prismatic or acicular, often in radial aggregates. However, a key indicator is its occurrence environment (agpaitic pegmatites) and associated minerals, such as aegirine, eudialyte, or arfvedsonite. ## Distinguishing from similar minerals Emeleusite can be confused with other pale silicates found in similar parageneses, such as natrolite, nepheline, or feldspars. However, natrolite is much softer (hardness approx. 5-5.5) and often forms thinner needles. Feldspars have different cleavage angles. Final and certain distinction often requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal forms It crystallizes in the orthorhombic system. It most often forms elongated, columnar or acicular crystals. They often occur as radial or chaotically arranged aggregates intergrown with other minerals, e.g., analcime.

Geological environment

## Genesis Emeleusite is a hydrothermal mineral, crystallizing in the late stages of pegmatite evolution associated with agpaitic nepheline syenites. It forms under low-temperature conditions from residual, rare-element-rich fluids. ## Mineral associations This mineral occurs in association with other rare alkaline minerals. The most common associations include: aegirine, albite, analcime, arfvedsonite, eudialyte, lorenzenite, microcline, natrolite, nepheline, pectolite, and sphalerite. ## Localities Emeleusite is known from only a few localities worldwide. The most important ones are: - Ilimaussaq alkaline complex, Greenland (type locality) - Mont Saint-Hilaire, Quebec, Canada - Khibiny Massif and Lovozero Massif, Kola Peninsula, Russia - Phonolite quarries in Aris, Namibia

Rarity

Very rare

For collectors

## Quality criteria The most highly valued emeleusite specimens are those that contain well-formed, sharply terminated, and transparent crystals with a distinct pink color. The contrasting rock matrix and the presence of other rare associated minerals are also very important. Radial crystal aggregates are particularly desirable. ## Popular localities Specimens from Mont Saint-Hilaire in Canada and from the massifs of the Kola Peninsula in Russia are the best known on the collector's market and fetch high prices due to crystal quality. Material from the type locality in Greenland is also highly sought after by specialists, although less frequently available.

Care and storage

## Cleaning Emeleusite specimens should be cleaned very carefully, using a soft brush and distilled water. Due to its good cleavage, ultrasonic cleaners should be avoided, as they could cause crystals to fracture along cleavage planes. ## What to avoid This mineral is sensitive to strong acids and bases. Avoid sudden temperature changes. Although relatively hard, it should be protected from impacts and contact with harder minerals to prevent scratches. ## Storage It is recommended to store specimens in separate, sealed boxes or display cases, which protects them from dust, mechanical damage, and excessive light. A locality label is crucial, as the collectible value of emeleusite is strongly linked to its origin.

Sources

IMA Mineral List (CNMNC)