Dickinsonite Mineral Overview

Mineral name: Dickinsonite
Mineral class: Phosphate

Known Facts

• Chemical formula: (Mn²⁺,Fe²⁺)₂Al(PO₄)₂(OH)₂·2H₂O (approximate; composition varies)
• Crystal system: Monoclinic
• Mohs hardness: 3–4
• Color range: Green, yellow-green, olive, brownish-green
• Luster: Vitreous to dull
• Streak: Pale green to white
• Cleavage: Poor
• Fracture: Uneven
• Specific gravity: Approximately 3.0–3.2
• Common locations: United States (New Hampshire), Brazil
• Uses: Collector specimens, mineralogical study
• Similar minerals: Eosphorite, childrenite, lithiophilite

Physical and Optical Characteristics

Dickinsonite typically occurs as:

• Granular or massive aggregates
• Occasionally as small prismatic crystals

It is usually opaque to translucent, with colors ranging from green to olive or brownish-green. The exact color depends on the relative proportions of manganese and iron.

The luster is generally vitreous, though it may appear dull in massive forms.

With a hardness of 3 to 4, Dickinsonite is relatively soft and can be scratched by harder silicate minerals.

Chemical Composition and Structure

Dickinsonite is a hydrated manganese–iron aluminum phosphate, with a variable composition:

• (Mn²⁺,Fe²⁺)₂Al(PO₄)₂(OH)₂·2H₂O

Key components include:

• Manganese (Mn²⁺) and iron (Fe²⁺)
• Aluminum (Al)
• Phosphate groups (PO₄³⁻)
• Hydroxyl (OH) and water (H₂O)

It is closely related to:

• Eosphorite (Mn-dominant)
• Childrenite (Fe-dominant)

Dickinsonite is often considered part of this phosphate mineral series, with intermediate compositions.

Formation and Geological Occurrence

Dickinsonite forms in granitic pegmatites, particularly in phosphate-rich zones.

Typical formation conditions include:

• Late-stage crystallization in pegmatitic systems
• Environments enriched in phosphorus, manganese, and iron

It is commonly associated with:

• Lithiophilite and triphylite
• Apatite
• Quartz and feldspar
• Other secondary phosphate minerals

It may form as part of the alteration sequence of primary lithium and manganese phosphates.

Common Locations

Notable occurrences of Dickinsonite include:

• United States: New Hampshire (type locality, from which the mineral is named)
• Brazil: Pegmatite deposits

It is a relatively rare mineral, typically found in specialized pegmatite environments.

Uses and Practical Significance

Dickinsonite has no industrial uses. Its importance lies in:

• Mineral collecting: Especially for collectors of pegmatite phosphates
• Scientific study: Understanding phosphate mineral evolution in pegmatites

Similar and Related Minerals

Dickinsonite may be confused with other phosphate minerals:

• Eosphorite: Typically pink and manganese-rich
• Childrenite: Brown, iron-rich counterpart
• Lithiophilite and triphylite: Primary phosphates in the same environment

Distinguishing Dickinsonite often requires:

• Chemical analysis
• Careful observation of color and associations

Identification Notes for Collectors

• Look for green to olive phosphate minerals in pegmatite environments
• Note association with lithiophilite, triphylite, and apatite
• Check for moderate softness (3–4)
• Observe granular or massive habit
• Use laboratory testing for accurate identification

Dickinsonite is a rare manganese–iron phosphate mineral, recognized for its occurrence in pegmatite phosphate assemblages and its relationship to the eosphorite–childrenite series.