Plumbogummite Mineral Overview

• Mineral name: Plumbogummite
• Mineral class: Phosphate
• Chemical formula: PbAl₃(PO₄)₂(OH)₅·H₂O
• Crystal system: Trigonal
• Mohs hardness: 4–4.5
• Color range: Blue, blue-green, green, gray
• Luster: Waxy to dull
• Streak: White
• Cleavage: Poor
• Fracture: Uneven to earthy
• Specific gravity: Approximately 3.0–3.3
• Transparency: Opaque to translucent
• Common locations: United States, Germany, China, Australia, United Kingdom
• Uses: Collector mineral, ornamental stone
• Similar minerals: Turquoise, variscite, wavellite

Naming and Classification

Plumbogummite is a lead aluminum phosphate mineral, belonging to the alunite supergroup, a family of minerals with similar structures but varying compositions.

The name comes from:

• plumbo- = lead
• gummite = gum-like texture

This reflects both its composition and its often smooth, waxy appearance.

Physical and Optical Characteristics

Plumbogummite typically occurs as:

• Botryoidal (rounded, grape-like) masses
• Crusts and coatings
• Earthy or compact aggregates

Well-formed crystals are rare.

Its most recognizable feature is its soft blue to blue-green color, often resembling:

• Turquoise
• Other secondary phosphate minerals

The luster is usually waxy or dull, giving it a smooth, slightly matte appearance.

With a Mohs hardness of 4 to 4.5, it is moderately soft.

Chemical Composition and Structure

Plumbogummite is composed of:

• Lead (Pb)
• Aluminum (Al)
• Phosphate groups (PO₄)
• Hydroxyl (OH)
• Water (H₂O)

It has a layered, hydrated structure, typical of alunite-group minerals, which contributes to:

• Its relatively low hardness
• Its botryoidal forms
• Its secondary formation

Formation and Geological Occurrence

Plumbogummite forms as a secondary mineral in the oxidized zones of lead deposits.

Typical formation conditions include:

• Weathering of primary lead minerals (such as galena)
• Interaction with phosphate-rich fluids
• Low-temperature, near-surface environments

It is commonly associated with:

• Pyromorphite
• Wavellite
• Goethite
• Other phosphate minerals

These associations reflect phosphate-rich, oxidized environments.

Common Locations

Plumbogummite is found in several regions:

• United States: Utah, Arizona, Pennsylvania
• Germany: Classic European deposits
• China: Modern collector specimens
• Australia and United Kingdom: Additional occurrences

Chinese specimens are especially known for vibrant color.

Uses and Practical Significance

Plumbogummite is valued for:

Collector Mineral

• Attractive color and botryoidal form
• Association with other phosphate minerals

Ornamental Use

• Occasionally cut or polished for display

It has no significant industrial use.

Similar and Related Minerals

Plumbogummite can resemble:

• Turquoise: Typically harder and more uniform
• Variscite: Usually greener and less waxy
• Wavellite: More radiating crystal structure

Color and texture are key distinguishing features.

Identification Notes for Collectors

• Look for blue to blue-green botryoidal material
• Note waxy luster and moderate softness (4–4.5)
• Observe earthy or smooth texture
• Check association with lead and phosphate minerals
• Confirm identity due to similarity with turquoise-like minerals

Plumbogummite is a secondary lead phosphate mineral, recognized for its blue-green color and botryoidal texture, making it a visually appealing and collectible mineral often compared to turquoise.