Mawbyite

Chemical formula: Pb²⁺Fe³⁺₂(As⁵⁺O₄)₂(OH)₂

Mawbyite is a rare lead and iron arsenate, forming characteristic reddish-brown, platy crystals.

## Characteristics Mawbyite is a rare mineral from the arsenate group, chemically classified as a basic lead and iron arsenate. It occurs as small, platy or wedge-shaped crystals, often aggregated into rosette-like or fan-shaped clusters. Its most distinctive feature is its intense reddish-brown to orange-brown color. ## Physical Properties Mawbyite crystals exhibit a luster ranging from vitreous to adamantine. The mineral is relatively dense due to its high lead content. It is translucent to opaque, and its Mohs hardness is approximately 4-5. ## Colors and Varieties The predominant and virtually only observed color of mawbyite is reddish-brown, transitioning into orange-brown shades. No color or commercial varieties are distinguished. ## History and Name The mineral was first described in 1987 by P.J. Bridge

Properties

Mohs hardness: 4
Color: Orange-brown, red-brown; rarely green
Luster: Adamantine, Vitreous
Streak: Orange-yellow
Density: 0
Cleavage: {001}, good.
Fracture: Conchoidal
Transparency: Transparent,Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Mawbyite is identified by its characteristic reddish-brown color, platy crystal habit, often forming fan-shaped aggregates, and high luster. Its occurrence in the oxidation zones of ore deposits, in association with other lead and iron arsenates, is also key. ## Distinguishing from Similar Minerals Mawbyite can be confused with other arsenates of similar color, such as carminite or segnitite. Differentiation often requires advanced analytical methods (XRD, EDS), although the characteristic crystal morphology of mawbyite (wedge-shaped plates in rosettes) can be a helpful clue. ## Crystal Forms Mawbyite crystals are usually very small, forming thin plates with a wedge or rhombic outline. They often intergrow into fan-shaped, rosette-like, or almost spherical aggregates.

Geological environment

## Genesis Mawbyite is a secondary mineral, forming in the oxidation zones (gossans) of polymetallic ore deposits rich in lead and arsenic. It forms as a result of the weathering of primary minerals such as galena and arsenopyrite. ## Mineral Associations It co-occurs with other secondary minerals of the oxidation zone, such as segnitite, plumogummite, hinsdalite, anglesite, cerussite, goethite, hematite, and quartz. ## Localities The most important and also the type locality for mawbyite is the Kintore mine in Broken Hill, New South Wales, Australia. It has also been identified in Tsumeb, Namibia, and several other locations worldwide, but specimens from Broken Hill remain exemplary.

Rarity

Very rare

For collectors

## Quality Criteria The most prized mawbyite specimens are characterized by well-formed, sharp crystals of intense reddish-brown color. Rosette-like or fan-shaped aggregates, contrasting with a light matrix rock (most often quartz), are highly valued. The size of crystals and aggregates also significantly affects value, as does the absence of damage. ## Popular Localities By far the most sought-after and classic specimens come from the type locality – the Kintore mine in Broken Hill, Australia. Specimens from this location are considered the standard for this mineral species.

Care and storage

## Cleaning Due to the presence of lead and arsenic, all activities should be performed with great caution, preferably with gloves. Specimens should only be dry-cleaned, using a soft brush or compressed air to remove dust. Avoid contact with water and any chemicals. ## What to Avoid Absolutely avoid contact with water, acids, and other solvents, which can damage the mineral. Mawbyite is sensitive to shocks and impacts. As a secondary mineral, it is unstable in changing chemical conditions. ## Storage Specimens should be stored in stable conditions, away from moisture and direct sunlight. The safest solution is a closed collector's box, away from other minerals that could scratch it.