Spangolite

Chemical formula: Cu₂+₆AlS₆+O₄(OH)₁₂Cl·₃H₂O

Spangolite is a rare, hydrated copper and aluminum sulfate, prized for its intensely greenish-blue, tabular or prismatic crystals.

## Characteristics Spangolite is a complex, hydrated copper, aluminum, and chlorine sulfate, belonging to the secondary minerals. It forms characteristic, well-developed, short prismatic or tabular crystals with a hexagonal outline. Its most recognizable feature is its intense, vivid color, ranging from emerald green to greenish-blue. The crystals exhibit a strong vitreous luster and are usually small, rarely exceeding a few millimeters in length. ## Physical Properties This mineral is relatively soft, with a hardness of about 3.5 on the Mohs scale, making it susceptible to scratching. Its density is approximately 3.14 g/cm³. Crystals are usually transparent to translucent, and their surfaces are characterized by a vitreous luster. It has good cleavage in one direction, and its fracture is conchoidal. ## Colors and Varieties Spangolite occurs in shades from emerald green, through greenish-blue, to dark green. Color is one of its main diagnostic and collector attributes. No named color or commercial varieties are distinguished. ## History and Name The mineral was first described in 1890 by Samuel Lewis Penfield. Its name honors Norman Spang (1841-1922), an American mineral collector from Pittsburgh, Pennsylvania, who provided the first specimens for study. The type locality is the Czar Mine in Tombstone, Cochise County, Arizona (USA). ## Uses Spangolite has no industrial applications. However, it is a valued and sought-after collector's mineral due to its rarity, attractive color, and well-formed crystals.

Properties

Mohs hardness: 3.5
Luster: Vitreous
Streak: Pale green
Density: 3.14
Cleavage: Good on {0001}
Fracture: Conchoidal
Transparency: Transparent to translucent
Crystal system: Trigonal

Diagnostic features

## Identification Key features for identifying spangolite are its trigonal crystal form (short prisms, tablets), intense greenish-blue color, vitreous luster, and relatively low hardness. Its paragenesis – occurrence in association with other secondary copper minerals – is also an important indicator. ## Distinguishing from Similar Minerals Spangolite can be confused with other green or blue minerals from the oxidation zone. It is distinguished from connellite by its crystal form – connellite most often forms acicular or radial aggregates. Brochantite also often occurs in acicular or fibrous forms. Euchroite, although similar in color, crystallizes in the orthorhombic system and has a slightly different hue. ## Crystal Forms Spangolite forms short prismatic crystals or thick tablets, often hemimorphic (crystal terminations at both ends are developed differently). It also occurs as crusts and mineral druses, which are clusters of small crystals covering the rock surface.

Geological environment

## Genesis Spangolite is a secondary mineral, formed in the oxidation (weathering) zones of copper ore deposits. Its formation is favored by dry or semi-arid climates. It forms as a result of complex chemical processes involving sulfate- and chloride-rich waters interacting with primary copper sulfides. ## Mineral Associations This mineral often co-occurs with other secondary copper minerals, such as azurite, malachite, cuprite, brochantite, connellite, linarite, as well as with gypsum, calcite, and quartz. ## Localities The most important spangolite localities in the world include the historic type locality in Tombstone, Arizona (USA), and the Majuba Hill Mine in Nevada (USA), which has yielded some of the best specimens. Other known localities include Cornish mines in Great Britain, deposits in Laurion, Greece, as well as Tsumeb in Namibia, and some deposits in Chile.

Rarity

Rare

For collectors

## Quality Criteria The most highly prized spangolite specimens are characterized by sharp, well-formed, and undamaged crystals of intense, emerald green or bluish-green color. Crystal transparency and size are also important – larger specimens are much rarer. The aesthetic placement of crystals on a rock matrix, especially in association with other contrasting minerals, enhances the specimen's appeal. ## Popular Localities Specimens from the type locality in Tombstone, Arizona, are considered classic. However, spangolites from the Majuba Hill Mine in Pershing County, Nevada, USA, are considered the best in the world in terms of crystal quality and size. Specimens from this locality command the highest prices in the collector's market.

Care and storage

## Cleaning Spangolite specimens should be cleaned very carefully, using a soft brush and distilled water. Due to its low hardness, mechanical cleaning can easily damage or scratch the crystal surfaces. Ultrasonic cleaners should not be used. ## What to Avoid Spangolite is soluble in acids, so contact with any chemicals should be avoided. It is also sensitive to high temperatures and sudden changes in temperature. It should be protected from scratching by harder minerals. ## Storage Collector specimens of spangolite are best stored in separate, padded boxes or display cases to avoid contact with other minerals. It should be protected from dust and direct, prolonged sunlight, and stored in a place with stable humidity.

Sources

IMA Mineral List (CNMNC)