Julgoldite-(Fe^2+^)

Chemical formula: Ca₂Fe₂+Fe₃+₂(Si₂O₇)(SiO₄)(OH)₂·H₂O

Julgoldite-(Fe²⁺) is a rare silicate from the pumpellyite group, forming dark green to black, acicular or radial crystalline aggregates.

## Characteristics Julgoldite-(Fe²⁺) is a mineral belonging to the pumpellyite group. It forms characteristic, small crystals with an acicular or bladed habit, which often arrange themselves into radial, fan-shaped, or spherulitic aggregates. Less commonly, it occurs as fibrous masses or compact masses. Its color is typically dark green, greenish-black to almost black, which is associated with the presence of iron ions at various oxidation states. Crystals are usually opaque, and only on thin edges can they be translucent. ## Physical Properties This mineral is characterized by a hardness of 4.5 on the Mohs scale and is relatively brittle. It has a vitreous luster, and in fibrous aggregates, a silky luster. Its density ranges from 3.56 to 3.61 g/cm³. It exhibits distinct, good cleavage in one direction. ## Colors and Varieties The dominant and essentially only color of julgoldite-(Fe²⁺) encountered is dark green in various shades, transitioning to blackish-green up to black. No color or commercial varieties are distinguished. ## History and Name The name "julgoldite" was given in 1966 by Moore and Ito in honor of Julian Royce Goldsmith (1918–1999), an American mineralogist and geochemist from the University of Chicago. The suffix "-(Fe²⁺)" specifies that the divalent iron ion dominates in a particular position in the crystal structure. The mineral was first described based on material from the Långban deposit in Sweden, which is its type locality. ## Uses Julgoldite-(Fe²⁺) has no industrial application. It is solely a mineral of scientific and collector's interest, sought after for its rarity and attractive crystalline forms.

Properties

Mohs hardness: 4.5
Luster: Vitreous, Silky
Streak: Greenish-gray
Density: 3.56-3.61
Cleavage: Good on {001}
Fracture: Uneven
Transparency: Translucent to opaque
Crystal system: Monoclinic

Diagnostic features

## Identification Julgoldite-(Fe²⁺) can be identified by its characteristic dark green to black color and typical forms of occurrence – radial or spherulitic aggregates composed of small, acicular or bladed crystals. Vitreous luster and a greenish-gray streak are also helpful features. ## Distinguishing from Similar Minerals It can be confused with other dark green minerals of similar habit, such as epidote, actinolite, or other minerals from the pumpellyite group. It is often distinguished from epidote by its more radial habit and slightly lower hardness. Actinolite tends to form fibrous aggregates rather than spherulitic ones. Final distinction from other members of the pumpellyite group (e.g., julgoldite-(Fe³⁺) or pumpellyite-(Mg)) requires advanced chemical analyses (EDS/WDS). ## Crystal Forms Crystals are elongated, bladed, or acicular, usually very small. Most often, they form radial, fan-shaped, spherulitic, or stellate aggregates. They also occur as fibrous, felted masses or as massive, compact vein fillings.

Geological environment

## Genesis Julgoldite-(Fe²⁺) is a low-temperature hydrothermal mineral. It forms in fissures and vugs of metamorphic rocks, especially in the greenschist facies, as well as in altered igneous rocks, such as basalts or diabases. It can also crystallize in the late stages of crystallization of some pegmatites or in skarns. ## Mineral Associations It often co-occurs with minerals such as apophyllite, prehnite, datolite, calcite, quartz, stilbite, and other zeolites, as well as with hematite and other minerals from the pumpellyite group. ## Localities The most important and classic localities for this mineral are Långban and Jakobsberg in Värmland (Sweden) – the type locality. It is also known from the Indian Queen mine in Snohomish County (Washington, USA), from the Pune and Mumbai regions in India (in vugs of Deccan basalts), and from the Wessels mine in Kuruman (South Africa).

Rarity

Rare

For collectors

## Quality Criteria The most valued by collectors are specimens with well-formed, distinct spherulites or radial aggregates of intense, dark green color. Contrast with a light matrix rock (e.g., white calcite or apophyllite) is important. The size of the aggregates and the absence of damage to the delicate acicular crystals significantly increase the value of the specimen. ## Popular Localities Specimens from the classic locality of Långban in Sweden have historical value. However, the most spectacular, large, and well-formed spherulites, often associated with apophyllite and stilbite, come from vugs in Deccan basalts in India (Pune, Nashik areas). High-quality specimens have also been found in South Africa (Wessels mine).

Care and storage

## Cleaning Julgoldite specimens should be cleaned very carefully, using a soft brush to remove dust. If necessary, compressed air can be used. Due to its brittleness and possible reactivity, washing in water is discouraged, and especially the use of any detergents or acids. ## What to Avoid Avoid contact with chemicals that could affect the iron ions in the mineral's structure. The mineral is brittle, so it must be protected from impacts and falls. It should not be heated or subjected to ultrasound in cleaners. ## Storage Collector's specimens of julgoldite are best stored in separate, padded boxes or display cases to avoid abrasions and mechanical damage. Due to the acicular or fibrous nature of the crystals, they should be handled gently to avoid crumbling delicate aggregates.

Sources

IMA Mineral List (CNMNC)