Metaköttigite

Chemical formula: (Zn₂+,Fe₃+)₃(As₅+O₄)₂·₈(H₂O,OH)

Hydrated zinc arsenate, a rare secondary mineral forming delicate, acicular crystals in the oxidation zones of ore deposits.

## Characteristics Metaköttigite is a hydrated zinc arsenate belonging to the symplesite group. It forms characteristic, fine, acicular or fibrous crystals, which often group into radial aggregates, rosettes, or form crusts and coatings. Individual crystals are usually too small to be observed with the naked eye, and their beauty is revealed only under magnification. Specimens typically appear as delicate, silky, or felt-like clusters on the surface of the host rock (matrix). ## Physical Properties This mineral is relatively soft, with a Mohs hardness of 2.5-3. It is brittle and has a low density, approximately 3.35 g/cm³. The luster on crystal surfaces is most often silky, and on fracture surfaces, it can also be pearly. It is a translucent mineral, becoming opaque in thicker aggregates. ## Colors and Varieties Metaköttigite usually occurs in shades of white – from pure white, through grayish-white, to yellowish-white. Some specimens may be colorless. No named color varieties or commercial varieties are distinguished. ## History and Name The mineral was first described in 1982 by H-J. Leyerzapf, W. Guse, and G. Tremmel. Its name refers to its close relationship with köttigite, from which it differs by a lower water content in its crystal structure (the prefix "meta-" indicates less hydration). ## Uses Metaköttigite has no industrial applications. It is valued solely as a collector's mineral and an object of scientific research.

Properties

Mohs hardness: 2.5-3
Luster: Silky to Pearly
Streak: White
Density: 3.35
Cleavage: Perfect on {010}
Fracture: Uneven
Transparency: Translucent to Opaque
Crystal system: Triclinic

Diagnostic features

## Identification Characteristic features of metaköttigite include its habit (fine, acicular crystals in radial clusters), silky luster, low hardness, and occurrence environment. It occurs in the oxidation zones of zinc and arsenic deposits, often on a limonitic matrix. ## Distinguishing from Similar Minerals Metaköttigite is visually indistinguishable from köttigite – this requires advanced analysis (e.g., X-ray diffraction) to determine the degree of hydration. It can be confused with other white, fibrous arsenates, such as parasymplesite (iron analogue) or erythrite (cobalt, but usually pink). It is distinguished from fibrous gypsum by its greater hardness and typical association with other arsenic minerals. ## Crystal Forms Crystals are elongated, acicular, or fibrous. They almost always occur in aggregates: radial, stellate, spherical (spherulites), or as crusts and coatings.

Geological environment

## Genesis Metaköttigite is a secondary mineral, forming in the oxidation (weathering) zones of hydrothermal polymetallic deposits rich in zinc and arsenic. It forms as a result of the alteration of primary ore minerals, such as sphalerite (source of zinc) and arsenopyrite or other arsenides (source of arsenic). ## Mineral Associations It most often co-occurs with the mineral from which its name is derived – köttigite. It is also accompanied by other secondary arsenates, such as adamite, legrandite, scorodite, and parasymplesite, as well as gypsum, calcite, and iron oxides (limonite, goethite). ## Localities This is a rare mineral. The most known and valued specimens by collectors come from the Ojuela Mine in Mapimí, Durango, Mexico. Other important localities include the Schneeberg area in Saxony (Germany), which is the type locality, and Lavrion in Greece.

Rarity

Rare

For collectors

## Quality Criteria The most highly valued specimens are those where metaköttigite forms rich, dense crusts composed of well-formed, radial aggregates. A contrasting, often dark, limonitic matrix highlights the white color and silky luster of the mineral. The size of the aggregates and the absence of damage to the delicate crystals are also important. ## Popular Localities Specimens from the Ojuela Mine in Mexico are by far the most sought after in the collector's market. They are characterized by exceptionally aesthetic, spherical aggregates with an intense silky luster.

Care and storage

## Cleaning Metaköttigite specimens are very delicate and sensitive to water. They should only be dry-cleaned, using a soft brush to remove dust. Compressed air can also be used from a safe distance to avoid damaging the fragile needles. Absolutely avoid ultrasonic cleaners. ## What to Avoid Avoid contact with water and any chemicals, as they can damage or dissolve the mineral. As an arsenate, it is toxic – avoid inhaling dust and wash hands after each contact. The mineral is sensitive to high temperatures, which can cause dehydration and destruction. Protect it from direct sunlight and physical impacts. ## Storage It is recommended to store specimens in closed, padded "perky boxes" to protect them from dust, moisture, and mechanical damage. Store in a dry place with a stable temperature.

Sources

IMA Mineral List (CNMNC)