Ferrisymplesite

Chemical formula: Fe₃+₃(As₅+O₄)₂(OH)₃·₅H₂O

Ferrisymplesite is a rare iron arsenate, forming characteristic spherical aggregates with a radial structure and a yellow-brown color.

## Characteristics Ferrisymplesite is a hydrated iron arsenate belonging to the symplesite group. It most commonly occurs as spherical or hemispherical aggregates with a radial-fibrous internal structure. Less frequently, it forms small, platy or acicular crystals. Its aggregates can also be earthy or form crusts. It is a product of the oxidation of arsenic-bearing minerals, especially in the weathering zones of iron and arsenic ores. ## Physical Properties Ferrisymplesite crystals are very small and delicate. This mineral is characterized by a silky or dull luster in the case of earthy aggregates. It is relatively soft and light. ## Colors and Varieties Ferrisymplesite ranges in color from yellow, through yellow-brown, reddish-brown, to brown. The color depends on the degree of oxidation and local chemical conditions. No named varieties are distinguished. ## History and Name The mineral's name, given in 1955, refers to its chemical composition – the dominance of iron (Latin: *ferrum*) and its connection to the structurally similar symplesite. It was first described based on material from the Tsumeb mine in Namibia and from Carrock Fell in Cumbria (England). ## Uses Due to its rarity and small crystal size, ferrisymplesite has no industrial application. It is of purely scientific and collector's interest, being a valued micromount mineral.

Properties

Mohs hardness: 2.5
Luster: Silky
Streak: Yellow-brown
Density: 3.14
Cleavage: Perfect on {010}
Fracture: Uneven
Transparency: Translucent
Crystal system: Monoclinic

Diagnostic features

## Identification Characteristic features include spherical aggregates with a radial, fibrous internal structure and a typical yellow-brown color. It occurs in the oxidation zones of arsenical deposits, which is a key field indicator. Identification often requires magnification. ## Distinguishing from Similar Minerals It can be confused with other secondary iron arsenates, such as scorodite or yukonite. It differs from scorodite in the form of aggregates (spherical aggregates vs. distinct crystals) and often in color. Yukonite is usually amorphous and has a more resinous or waxy appearance. Final distinction requires chemical (EDS) or X-ray (XRD) analysis. ## Crystal Forms Most commonly, it forms radial-fibrous, spherical aggregates. Single, elongated, platy crystals gathered in rosette-like or chaotic groups are rarely found.

Geological environment

## Genesis Ferrisymplesite is a secondary mineral, formed in the oxidation (weathering) zones of ore deposits rich in arsenic, especially arsenopyrite. It forms under low temperature and pressure conditions as a result of the reaction of surface waters with primary minerals. ## Mineral Associations It often co-occurs with other minerals from the oxidation zone, such as scorodite, pharmacosiderite, arsenopyrite, pyrite, as well as various iron oxides (e.g., goethite, hematite). ## Localities Key localities worldwide include the Tsumeb mine (Namibia), Carrock Fell (Cumbria, England), Ogonja mine (Okayama Prefecture, Japan), as well as numerous occurrences in the Ore Mountains region of Saxony (Germany) and in Lavrion (Greece).

Rarity

Rare

For collectors

## Quality Criteria The most valued specimens by collectors are those with well-formed, distinct spherical aggregates of intense, yellow-brown color, contrasting with the rock matrix. The absence of damage to the delicate, fibrous structures is important. Due to the microscopic nature of most occurrences, the aesthetic composition within the microscope's field of view is crucial. ## Popular Localities Specimens from Tsumeb in Namibia and from the Japanese Ogonja mine are considered classic and most desirable due to their quality and historical significance.

Care and storage

## Cleaning Specimens should be handled with utmost care. Cleaning is highly inadvisable due to fragility and potential water solubility. If absolutely necessary, a stream of compressed air from a distance or a very soft brush can be used very gently. ## What to Avoid Contact with water, acids, and other chemicals that can damage or dissolve the mineral should be strictly avoided. Avoid ultrasound, vibrations, and sudden temperature changes. Protect from direct sunlight, which can cause fading. ## Storage It is recommended to store specimens exclusively in specialized micromount boxes to protect them from dust, mechanical damage, and humidity. Display should be under glass, in stable conditions.

Sources

IMA Mineral List (CNMNC)