Descloizite Mineral Overview

Mineral name: Descloizite
Mineral class: Vanadate

Known Facts

• Chemical formula: Pb(Zn,Cu)(VO₄)(OH)
• Crystal system: Orthorhombic
• Mohs hardness: 3–3.5
• Color range: Brown, reddish-brown, orange-brown, nearly black
• Luster: Resinous to subadamantine
• Streak: Yellow to orange-yellow
• Cleavage: Poor
• Fracture: Uneven to subconchoidal
• Specific gravity: Approximately 5.9–6.2
• Common locations: Namibia, Morocco, Mexico, United States
• Uses: Collector specimens, minor vanadium ore
• Similar minerals: Mottramite, vanadinite, wulfenite

Physical and Optical Characteristics

Descloizite typically occurs as:

• Botryoidal (rounded) masses
• Crusts and coatings
• Radiating fibrous aggregates
• Occasionally as small prismatic crystals

It is usually opaque, with colors ranging from brown to reddish-brown or nearly black. Some specimens show orange-brown tones.

The luster is commonly resinous, sometimes approaching subadamantine, especially on fresh surfaces.

A key identifying feature is its yellow to orange-yellow streak, which contrasts with its darker external color.

Chemical Composition and Structure

Descloizite is a lead zinc vanadate hydroxide, with the formula:

• Pb(Zn,Cu)(VO₄)(OH)

Key components include:

• Lead (Pb)
• Zinc (Zn), sometimes partially replaced by copper (Cu)
• Vanadate groups (VO₄³⁻)
• Hydroxyl (OH)

It forms a solid solution series with:

• Mottramite (PbCu(VO₄)(OH)) — copper-dominant endmember

Intermediate compositions between zinc- and copper-rich varieties are common, making precise identification sometimes dependent on chemical analysis.

Formation and Geological Occurrence

Descloizite forms as a secondary mineral in the oxidation zones of lead–zinc–vanadium deposits.

Typical formation conditions include:

• Weathering of primary sulfide minerals
• Interaction with vanadium-bearing solutions
• Deposition in oxidizing environments

It commonly occurs in:

• Arid and semi-arid regions, where oxidation processes are active

Associated minerals include:

• Vanadinite
• Mottramite
• Wulfenite
• Cerussite
• Iron oxides

Common Locations

Notable occurrences of Descloizite include:

• Namibia: Berg Aukas and other localities (well-known specimens)
• Morocco: Vanadium-rich deposits
• Mexico: Oxidized lead deposits
• United States: Arizona, New Mexico

Namibia is especially известна for high-quality botryoidal specimens.

Uses and Practical Significance

Descloizite has limited economic importance but is notable for:

• Collector specimens: Valued for botryoidal forms and luster
• Vanadium source: Minor ore in some deposits

Vanadium is used in:

• Steel alloys
• Chemical applications

However, descloizite is not a primary commercial source.

Similar and Related Minerals

Descloizite may be confused with:

• Mottramite: Copper-rich and often greener
• Vanadinite: Typically red to orange with hexagonal crystals
• Wulfenite: Bright orange to yellow tabular crystals

Distinguishing features include:

• Brown coloration
• Yellow streak
• Botryoidal habit

Identification Notes for Collectors

• Look for brown to reddish botryoidal coatings in oxidized ore zones
• Check for yellow to orange-yellow streak
• Note association with vanadinite and wulfenite
• Observe resinous luster
• Consider chemical testing to distinguish from mottramite

Descloizite is a secondary vanadate mineral, recognized for its brown botryoidal forms and association with vanadium-rich oxidation zones, and is primarily valued by collectors.