Jamborite

Chemical formula: Ni<sup>2+</sup><sub>1-x</sub>Co<sup>3+</sup><sub>x</sub>(OH)<sub>2-x</sub>(S<sup>6+</sup>O<sub>4</sub>)<sub>x</sub>·nH<sub>2</sub>O [x ≤ 1/3; n ≤ (1-x)]

Jamborite is a rare, secondary nickel mineral with a characteristic apple-green color, most often forming microcrystalline coatings and crusts.

## Characteristics Jamborite is a hydrated nickel and cobalt hydroxy-sulfate, belonging to the hydrotalcite group. It occurs as very fine, microscopic crystals that form earthy or chalky coatings, crusts, and fillings in small rock fissures. Due to its microcrystalline nature, individual crystals are rarely visible to the naked eye. It is most often observed as soft, porous aggregates with a dull appearance. ## Physical Properties This mineral is very soft; its Mohs hardness is only about 1, meaning it can be scratched with a fingernail. It has a very low density, approximately 2.68 g/cm³, and even below 2.0 g/cm³ when dried. It is characterized by a dull or earthy luster and is usually opaque. ## Colors and Varieties Jamborite occurs in a characteristic light green or apple-green color, which is typical for hydrated nickel minerals. No color or commercial varieties are distinguished. ## History and Name The mineral's name honors John Leslie Jambor (1936–2008), a Canadian mineralogist who made significant contributions to the study of sulfate and arsenate minerals, and was also one of the co-authors of the first description of jamborite. The mineral was approved by the IMA in 1971, and its discovery was made in Italy, at the Ca' de' Candi mine near Bologna. ## Uses Jamborite has no industrial application. It is solely an object of interest for collectors specializing in rare minerals or mineralogical systematics.

Properties

Mohs hardness
1
Luster
Dull
Streak
Light green
Density
2.68
Cleavage
Perfect on {0001}
Fracture
Uneven
Transparency
Opaque
Crystal system
Trigonal

Diagnostic features

## Identification Jamborite can be preliminarily identified by its characteristic apple-green color, very low hardness (about 1 on the Mohs scale), and occurrence as earthy, soft coatings and crusts. It often forms pseudomorphs after millerite, retaining its acicular shape. ## Distinguishing from Similar Minerals Jamborite is sometimes confused with other secondary nickel minerals, such as annabergite or gaspeite. It is distinguished from annabergite by the lack of distinct crystals and often a lighter shade. From gaspeite, which is a carbonate, it is distinguished by its reaction with acids (gaspeite reacts more vigorously). However, certain identification requires advanced analytical methods, such as X-ray diffraction (XRD). ## Crystal Forms It forms microscopic, hexagonal plates and flakes that aggregate into rosette-like or spherulitic clusters. It commonly occurs as pseudomorphs after hexagonal or acicular millerite crystals, retaining their external form but filling them with porous, earthy material.

Geological environment

## Genesis Jamborite is a secondary mineral, formed in oxidation (weathering) zones of nickel-rich ore deposits, especially in the presence of sulfides such as millerite, siegenite, or polydymite. It forms at low temperatures as a result of surface water acting on primary nickel minerals in ultramafic rocks (serpentinites) and sedimentary rocks. ## Mineral Associations It most often co-occurs with minerals from which it forms or which accompany it in the oxidation zone. These are primarily millerite (often as pseudomorphs after it), calcite, dolomite, magnesite, as well as other secondary nickel and cobalt minerals such as annabergite, gaspeite, reevesite, and honessite. ## Localities The most important jamborite localities worldwide include the Ca' de' Candi mine in Emilia-Romagna (Italy) - the type locality; numerous localities in Pennsylvania (USA), e.g., in Lancaster County; Mont-Saint-Hilaire in Quebec (Canada); the Jacupiranga mine in São Paulo (Brazil); and nickel deposits near Frankenstein (Ząbkowice Śląskie) in Lower Silesia (Poland).

Rarity

Rare

For collectors

## Quality Criteria The most valued by collectors are specimens showing clear and complete pseudomorphs of jamborite after well-formed millerite crystals, especially those forming attractive, acicular groups. An intense, apple-green color and the absence of damage to the delicate structure are also important. Specimens on a contrasting rock matrix are rated higher than loose fragments. ## Popular Localities Localities in Pennsylvania, USA (especially from quarries in Lancaster County), are considered classic and provide the best quality specimens, from which world-renowned pseudomorphs after millerite originate. Italian specimens from the type locality are also sought after for historical reasons.

Care and storage

## Cleaning Jamborite specimens are extremely delicate and fragile. Mechanical cleaning, including the use of brushes, should be avoided. If absolutely necessary, the specimen can be carefully rinsed in distilled water and then left to dry completely at room temperature, without the use of heat sources. ## What to Avoid Jamborite is sensitive to acids and other chemicals. Contact with any cleaning agents should be avoided. As a hydrated mineral, it can lose water at elevated temperatures, leading to its destruction. It should be protected from high temperatures and direct sunlight. ## Storage It is recommended to store specimens in closed, padded collector boxes to protect them from mechanical damage, dust, and sudden changes in humidity. Due to its softness, it should not be stored in contact with harder minerals.

External references

Sources

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