Aegirine

Chemical formula: NaFe₃+Si₂O₆

Aegirine is a sodium iron silicate, belonging to the pyroxene group, often characterized by elongated, dark green crystals.

## Characteristics Aegirine is a mineral from the pyroxene group, a sodium iron silicate. Typical aegirine specimens occur as elongated, prismatic crystals, often with rhombic or hexagonal cross-sections. These crystals can be thin and acicular, forming radial or fibrous aggregates. The color of aegirine is usually dark green to greenish-black, although reddish-brown or black specimens are also found. Crystal surfaces may exhibit a characteristic vitreous or resinous luster. ## Physical Properties The Mohs hardness of aegirine is 6. This mineral exhibits good cleavage along the {110} planes. The density of aegirine is approximately 3.5 g/cm³. The luster is usually vitreous, sometimes resinous. Aegirine can be transparent to opaque. ## Colors and Varieties Aegirine most commonly occurs in shades of dark green, transitioning to greenish-black. Reddish-brown and black colors are also possible. No specific commercial varieties of aegirine are distinguished, however, its color and crystal form may vary depending on the locality. ## History and Name Aegirine was described in 1821. Its name comes from Ægir, the Norse god of the sea, referring to the discovery site of the first specimens in Norway, near the coast. ## Applications Aegirine has no significant industrial applications. It is primarily valued by mineral collectors due to its aesthetic crystals and the rarity of well-formed specimens.

Properties

Mohs hardness: 6
Luster: Vitreous, resious
Streak: Pale yellowish grey
Density: 3.5
Cleavage: Good on {110}
Fracture: Nierówny do muszlowego
Transparency: Transparent,Opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Aegirine can be identified by its characteristic dark green to black color, elongated, prismatic crystals, and vitreous or resinous luster. A Mohs hardness of 6 is also a diagnostic feature. The streak of aegirine is pale yellowish-gray. ## Distinguishing from Similar Minerals Aegirine can be confused with other dark minerals such as hornblende or arfvedsonite. It is distinguished from hornblende by its typically more distinct cleavage at angles of approximately 87 and 93 degrees (in pyroxenes) compared to approximately 56 and 124 degrees (in amphiboles), as well as the absence of the fibrous habit typical of amphiboles. It differs from arfvedsonite in chemical composition and often a greener hue. ## Crystal Forms Aegirine most commonly forms elongated, columnar, or acicular crystals, often with rhombic or hexagonal cross-sections. These crystals can occur individually, form radial aggregates, or dense, fibrous masses.

Geological environment

## Genesis Aegirine primarily forms in alkaline igneous rocks, such as nepheline syenites, phonolites, and trachytes, as well as in pegmatites and hydrothermal veins associated with these rocks. It can also occur in some metamorphic rocks that have undergone sodic metasomatism. ## Mineral Associations Aegirine often co-occurs with other alkaline minerals, such as nepheline, sodalite, arfvedsonite, microcline, albite, zircon, titanite, and astrophyllite. ## Localities Known localities for aegirine include Norway (Langesundsfjord), Russia (Kola Peninsula, Khibiny), Canada (Mont Saint-Hilaire in Quebec), USA (Arkansas), Greenland, Malawi, and South Africa.

Rarity

Very Common

For collectors

## Quality Criteria The most prized aegirine specimens are those with well-formed, large, undamaged crystals of intense, dark green color and distinct luster. Radial aggregates or druses with aesthetically arranged crystals are also highly valued. Transparency and lack of inclusions increase the specimen's value. ## Popular Localities The most sought-after aegirine specimens come from Norway, especially from the Langesundsfjord area, where some of the first and best-formed crystals were found. Other valued localities include the Kola Peninsula in Russia and Mont Saint-Hilaire in Canada.

Care and storage

## Cleaning Aegirine can be cleaned using a soft brush and lukewarm water. For more stubborn dirt, a mild soap may be used. After washing, rinse the mineral thoroughly with clean water and dry with a soft cloth. ## What to Avoid Avoid using strong chemicals, acids, and bases, which can damage the mineral's surface. Aegirine is not particularly sensitive to sunlight or typical temperature changes, but extreme conditions can be harmful. Prolonged exposure to high humidity is not recommended. ## Storage Aegirine should be stored in a dry place, away from dust and other minerals that could scratch it. Ideally, the specimen should be placed in a closed display case or a box with soft padding. Larger, stable specimens can be displayed on an open shelf, provided they are regularly dusted.