Maricopaite

Chemical formula: Ca<sub>2</sub>Pb<sup>2+</sup><sub>7</sub>(Si<sub>36</sub>Al<sub>12</sub>)O<sub>99</sub>·n(H<sub>2</sub>O,OH)

Maricopaite is a very rare, lead-bearing zeolite group mineral, forming white, fibrous aggregates.

## Characteristics Maricopaite is a hydrated lead and calcium silicate, belonging to the zeolite group. It occurs as delicate, fibrous or platy crystals, which typically form radial or tangled aggregates. Individual crystals are very small, rarely exceeding 1 mm in length. Due to its delicate nature, specimens are extremely fragile. ## Physical Properties Maricopaite crystals exhibit a silky luster. This mineral is soft, with a Mohs hardness of approximately 2. It is translucent to transparent. Its density is relatively high for a silicate, around 3.55 g/cm³, which is a result of its high lead content. ## Colors and Varieties Maricopaite is usually colorless or white. No colored or commercial varieties have been identified. ## History and Name The mineral was discovered in the Moon Anchor Mine (formerly Big Horn Mine), in the Big Horn Mountains, Maricopa County, Arizona, USA. Its name, approved by IMA in 1989, comes from the name of the county where the type locality is situated. It was first described by William W. Pinch, Peter C. Dunn, George E. Harlow, and Jerry L. Grice. ## Uses Maricopaite has no industrial application. It is solely a mineral of scientific and collector interest, sought after for its rarity and attractive, fibrous forms.

Properties

Mohs hardness
2
Luster
Silky
Streak
White
Density
3.55
Cleavage
Perfect on {010}
Fracture
Uneven
Transparency
Transparent to translucent
Crystal system
Orthorhombic

Diagnostic features

## Identification Maricopaite is identified by its characteristic white, silky aggregates with a radial or tangled structure. Its occurrence in association with other rare lead minerals in oxidized ore zones is a key indicator. High density, unusual for minerals with a fibrous appearance, can also be helpful. ## Distinguishing from Similar Minerals Maricopaite can be confused with other white, fibrous minerals, such as some zeolites (e.g., natrolite, mesolite) or secondary oxidation zone minerals (e.g., acicular cerussite). Differentiation often requires advanced analytical methods, such as X-ray diffraction (XRD). Association with other lead minerals at a given locality is an important distinguishing factor. ## Crystal Forms The mineral forms very fine, acicular or platy crystals, elongated along the [001] axis. These crystals combine into radial, stellate, or tangled aggregates, as well as cotton-like masses.

Geological environment

## Genesis Maricopaite is a secondary mineral, formed in the oxidation zones (gossans) of polymetallic ore deposits rich in lead. It forms in rock cavities and fissures as a result of low-temperature hydrothermal processes or the weathering of primary lead minerals. ## Mineral Associations At the type locality (Moon Anchor Mine, Arizona), maricopaite co-occurs with minerals such as cerussite, wulfenite, anglesite, phosgenite, laurionite, leadhillite, alamosite, dioptase, as well as quartz, calcite, and hematite. ## Localities The most important and type locality for maricopaite is the Moon Anchor Mine (Big Horn Mine) in Maricopa County, Arizona, USA. This is the only confirmed locality from which well-characterized specimens of this mineral originate.

Rarity

Very rare

For collectors

## Quality Criteria The most prized maricopaite specimens are those with well-formed, rich radial aggregates on a contrasting rock matrix. The size and completeness of the aggregates and the absence of damage to the delicate fibers are important. A pure, white color and silky luster enhance the specimen's attractiveness. Due to its extreme rarity, any well-formed specimen is considered valuable. ## Popular Localities The only source of collector specimens is the type locality – the Moon Anchor Mine in Arizona, USA. Material from this location is extremely rare on the market.

Care and storage

## Cleaning Maricopaite is extremely delicate and fragile. Mechanical or chemical cleaning is not recommended. Any attempts at cleaning, even with water, can destroy the delicate, fibrous crystals. It is best to leave the specimen in the state in which it was found. ## What to Avoid Avoid any contact with water, chemicals, ultrasound, and sudden temperature changes. The mineral is very sensitive to vibrations and shocks, which can cause the aggregates to disintegrate. ## Storage Maricopaite specimens should be stored in closed, padded boxes to protect them from dust, shocks, and mechanical damage. It should not be displayed in open showcases. Due to its lead content, it is advisable to store it away from children and wash hands after any contact.

Sources

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