Bunsenite

Chemical formula: Ni²⁺O

Bunsenite is a rare nickel oxide from the periclase group, forming characteristic, isometric crystals of an intensely green color.

## Characteristics Bunsenite is a nickel oxide (NiO) belonging to the periclase group. It occurs as well-formed, small, isometric crystals – most often cubes, octahedra, and rhombic dodecahedra. These crystals rarely exceed 1-2 mm in size. The mineral also forms granular aggregates and coatings. Its most characteristic feature is its vivid green color, from which its historical name "nickel green" originates. ## Physical Properties Bunsenite is a hard mineral, with a Mohs hardness of 5.5. It is characterized by a vitreous to sub-adamantine luster. It is transparent to translucent. Its density is significant, ranging from 6.4 to 6.95 g/cm³, which is noticeable even in small specimens. ## Colors and Varieties This mineral occurs in a characteristic color range from pistachio green, through emerald green, to dark green, and even greenish-black. No distinct color or commercial varieties are recognized. ## History and Name Bunsenite was first described in 1868 by the Irish mineralogist and chemist James Emerson Reynolds. He named the mineral in honor of Robert Wilhelm Bunsen (1811-1899), a famous German chemist who was the first to synthesize artificial nickel oxide and describe its crystallographic and physical properties. Type specimens originate from the mine in Johanngeorgenstadt, Saxony (Germany). ## Uses Due to its extreme rarity, bunsenite has no industrial applications. It is solely an object of interest for collectors specializing in rare minerals and for scientific institutions.

Properties

Mohs hardness: 5.5
Color: Dark pistachio-green
Luster: Vitreous to adamantine
Streak: Brownish-black
Density: 6.898
Cleavage: Perfect on {100}, good on {110}
Fracture: Uneven
Transparency: Transparent
Crystal system: Isometric

Diagnostic features

## Identification The key diagnostic feature of bunsenite is its intensely green color combined with the regular, cubic form of its crystals. High density, hardness, and vitreous luster are also helpful in identification. Its occurrence in association with other nickel and bismuth minerals is also characteristic. ## Distinguishing from Similar Minerals Bunsenite is sometimes confused with other green secondary nickel minerals, such as annabergite or zaratite. However, annabergite has a much lower hardness (1.5-2.5) and forms acicular or fibrous aggregates. Zaratite is amorphous and occurs as crusts or spherical aggregates with lower hardness (approx. 3). It is distinguished from more common minerals like dioptase or some garnets by its crystal form and occurrence environment. ## Crystal Forms Bunsenite crystallizes in the isometric system, forming classic, isometric shapes. Cubes, octahedra, and their combinations are most commonly found. Crystals are usually small but well-formed.

Geological environment

## Genesis Bunsenite is a hydrothermal mineral, formed by the alteration of primary nickel ores, such as nickeline. It forms in ore veins, often in paragenesis with bismuth and uranium minerals. It can also form as a result of volcanic activity (as a product of volcanic exhalations) and in zones of underground fires, where nickel-bearing rocks are calcined. ## Mineral Associations This mineral often co-occurs with nickeline, native bismuth, bismuthinite, annabergite, zaratite, aerugite, quartz, hematite, and uraninite. The association with native bismuth and nickeline is particularly characteristic of its type locality in Germany. ## Localities The most important and historical locality, from which the best-formed crystals originate, is Johanngeorgenstadt in the Ore Mountains (Saxony, Germany). Other known localities include the Cobalt-Gowganda district in Ontario (Canada), the South Terras mine in Cornwall (United Kingdom), and some volcanoes, e.g., Tolbachik in Kamchatka (Russia), where it forms as a sublimation product.

Rarity

Very rare

For collectors

## Quality Criteria The most highly prized bunsenite specimens are those with sharp, well-formed crystals of regular, cubic or octahedral shape. The intensity and purity of the green color and the transparency of the crystals are crucial. Specimens where single, undamaged crystals are clearly exposed on a contrasting matrix (e.g., on quartz or native bismuth) achieve the highest value. Crystal size is also an important factor – any specimen with crystals exceeding 1 mm is considered exceptional. ## Popular Localities Specimens from the classic locality in Johanngeorgenstadt, Germany, are by far the most sought after by collectors. They are considered the global standard for this mineral. Specimens from other localities, though also valuable from a scientific perspective, rarely match the quality of the German ones.

Care and storage

## Cleaning Bunsenite specimens should be cleaned mechanically only, using a soft brush to remove dust. Due to its reactivity with acids, the use of any chemical agents is absolutely inadvisable. If necessary, a small amount of distilled water can be used, and the specimen should be thoroughly dried immediately. ## What to Avoid Avoid contact with all acids, which can damage or completely dissolve the mineral. Do not heat it or expose it to sudden temperature changes. Prolonged exposure to moisture is also inadvisable. ## Storage Bunsenite is best stored in stable conditions, in a closed display case or a "membrane box" type container, which protects it from dust, moisture, and mechanical damage. Due to the small size of the crystals, this is the best way to safely display them.