Herderite Mineral Overview

• Mineral name: Herderite
• Mineral class: Phosphate
• Chemical formula: CaBePO₄(F,OH) (calcium beryllium phosphate fluoride hydroxide)
• Crystal system: Monoclinic
• Mohs hardness: 5–5.5
• Color range: Colorless, white, yellow, pale green
• Luster: Vitreous
• Streak: White
• Cleavage: Perfect (one direction)
• Fracture: Uneven
• Specific gravity: Approximately 2.9–3.0
• Transparency: Transparent to translucent
• Common locations: Brazil, Germany, United States, Namibia
• Uses: Collector mineral, rare gemstone
• Similar minerals: Hurlbutite, apatite, beryl

Naming and Classification

Herderite is a calcium beryllium phosphate mineral, named after Sigmund August Wolfgang von Herder, a German mining official.

It forms a series with:

• Hydroxylherderite (OH-dominant)
• Herderite (F-dominant)

These minerals differ based on the relative amounts of fluorine and hydroxyl in their structure.

Physical and Optical Characteristics

Herderite typically occurs as:

• Tabular to prismatic crystals
• Wedge-shaped or flattened crystals

Its color is usually:

• Colorless
• Pale yellow
• Light green

The luster is vitreous, giving crystals a glassy appearance.

With a Mohs hardness of 5–5.5, it is moderately hard.

Crystal Habit (Key Feature)

Herderite is known for:

• Distinctive wedge-shaped or flattened crystals

These crystals often appear:

• Elongated or slightly curved

Chemical Composition and Structure

Herderite is composed of:

• Calcium (Ca)
• Beryllium (Be)
• Phosphate (PO₄)
• Fluorine (F) and hydroxyl (OH)

It has a phosphate-based structure, with:

• Beryllium and calcium coordinated within the framework

Formation and Geological Occurrence

Herderite forms in granitic pegmatites, particularly:

Rare-Element Pegmatites

• Enriched in beryllium and phosphorus

Typical formation conditions include:

• Late-stage crystallization of magma
• Concentration of rare elements

It is commonly associated with:

• Beryl
• Quartz
• Feldspar
• Other phosphate minerals

Common Locations

Herderite is found in several notable regions:

• Brazil: Major source of gem-quality material
• Germany: Classic occurrences
• United States: Maine and New Hampshire
• Namibia: Additional deposits

Brazilian specimens are especially well known.

Uses and Practical Significance

Herderite is valued for:

Collector Mineral

• Well-formed crystals
• Occurrence in pegmatites

Gemstone Use

• Occasionally faceted
• Rare due to limited availability

It has no industrial use.

Similar and Related Minerals

Herderite can resemble:

• Hurlbutite: Similar composition but different structure
• Apatite: More common phosphate mineral
• Beryl: Harder and more durable

Careful identification may require analysis.

Identification Notes for Collectors

• Look for tabular or wedge-shaped pale crystals
• Note moderate hardness (5–5.5)
• Observe vitreous luster
• Check association with pegmatites
• Consider presence of beryllium minerals

Herderite is a calcium beryllium phosphate mineral, recognized for its occurrence in rare-element pegmatites and its distinctive crystal habit, making it a specialized and collectible mineral.