Legrandite Mineral Overview

• Mineral name: Legrandite
• Mineral class: Arsenate
• Chemical formula: Zn₂AsO₄(OH)·H₂O (zinc arsenate hydroxide hydrate)
• Crystal system: Monoclinic
• Mohs hardness: 4.5–5
• Color range: Bright yellow, golden yellow, yellow-orange
• Luster: Vitreous
• Streak: Pale yellow
• Cleavage: Good
• Fracture: Uneven
• Specific gravity: Approximately 3.2–3.4
• Transparency: Transparent to translucent
• Common locations: Mexico (primary), Namibia
• Uses: Collector mineral
• Similar minerals: Adamite, mimetite, wulfenite

Naming and Classification

Legrandite is a zinc arsenate mineral, named after Louis C. Legrand, a Belgian mining engineer.

It belongs to a group of secondary arsenate minerals that form in oxidized ore environments, particularly where zinc and arsenic are present.

Physical and Optical Characteristics

Legrandite typically occurs as:

• Slender prismatic crystals
• Radiating sprays or clusters
• Delicate, elongated crystal groups

Its most striking feature is its vivid yellow color, which can appear:

• Bright lemon yellow
• Golden yellow
• Slightly orange-yellow

The luster is vitreous, giving crystals a bright, glassy appearance.

With a Mohs hardness of 4.5–5, it is moderately soft and somewhat fragile.

Crystal Habit (Key Feature)

Legrandite is especially known for:

• Radiating sprays of elongated crystals
• Elegant, fan-like or starburst arrangements

These formations make it highly desirable among collectors.

Chemical Composition and Structure

Legrandite is composed of:

• Zinc (Zn)
• Arsenate (AsO₄)
• Hydroxyl (OH)
• Water (H₂O)

Its structure includes:

• Chains of linked arsenate groups
• Water molecules within the crystal lattice

Formation and Geological Occurrence

Legrandite forms as a secondary mineral in oxidized zones of zinc deposits, particularly:

Oxidation Zones

• Weathering of primary zinc ores
• Interaction with arsenic-bearing fluids

Typical formation conditions include:

• Near-surface environments
• Oxidizing conditions
• Presence of zinc and arsenic

It is commonly associated with:

• Adamite
• Smithsonite
• Hemimorphite
• Other arsenate minerals

Common Locations

Legrandite is rare and found in limited localities:

• Mexico: Ojuela Mine, Durango (world-famous specimens)
• Namibia: Tsumeb Mine

Mexican specimens are especially prized for their bright color and crystal quality.

Uses and Practical Significance

Legrandite has no industrial use due to its rarity and arsenic content.

It is highly valued for:

Collector Mineral

• Brilliant color
• Attractive crystal sprays
• Rarity

Safety Considerations

Legrandite contains arsenic, so:

• Avoid inhaling dust
• Do not ingest
• Wash hands after handling

Display specimens are generally safe if handled properly.

Similar and Related Minerals

Legrandite can resemble:

• Adamite: Often greener and more common
• Mimetite: Typically heavier and more orange-yellow
• Wulfenite: Usually forms tabular crystals rather than sprays

Crystal habit and color help distinguish legrandite.

Identification Notes for Collectors

• Look for bright yellow, radiating crystal sprays
• Note moderate hardness (4.5–5)
• Observe vitreous luster
• Consider association with zinc and arsenate minerals
• Recognize rarity and typical Mexican origin

Legrandite is a zinc arsenate mineral, recognized for its brilliant yellow color and elegant crystal sprays, making it one of the most visually striking and desirable minerals for collectors.