Diaspore Mineral Overview
Mineral name: Diaspore
Mineral class: Oxide (hydroxide subgroup)
Known Facts
- Chemical formula: AlO(OH)
- Crystal system: Orthorhombic
- Mohs hardness: 6.5–7
- Color range: Colorless, white, gray, yellow, brown, green
- Luster: Vitreous to pearly
- Streak: White
- Cleavage: Perfect in one direction
- Fracture: Uneven to splintery
- Specific gravity: Approximately 3.3–3.5
- Common locations: Turkey, Russia, China, United States, Greece
- Uses: Aluminum ore (minor), gemstones (rare), collector specimens
- Similar minerals: Boehmite, gibbsite, corundum
Physical and Optical Characteristics
Diaspore typically occurs as:
- Tabular or blade-like crystals
- Lamellar or foliated aggregates
- Massive forms in bauxite deposits
Crystals are often transparent to translucent, especially in gem-quality material.
Color ranges from colorless and white to yellow, brown, or green, depending on impurities.
The luster is vitreous on crystal faces and pearly on cleavage surfaces.
A defining feature is its perfect cleavage, which makes the mineral:
- Brittle and prone to splitting, even though it has relatively high hardness
Chemical Composition and Structure
Diaspore has the formula:
- AlO(OH)
It is an aluminum oxide-hydroxide, closely related to:
- Boehmite (AlO(OH))
- Gibbsite (Al(OH)₃)
These minerals differ in:
- Crystal structure
- Water content
- Physical properties
The structure of diaspore consists of:
- Aluminum coordinated with oxygen and hydroxyl groups
- A tightly bonded arrangement, contributing to its relatively high hardness
Formation and Geological Occurrence
Diaspore forms in several geological environments:
Bauxite deposits
- Common component of bauxite, the primary aluminum ore
- Forms through intense weathering of aluminum-rich rocks
Metamorphic environments
- Found in:
- High-pressure metamorphic rocks
- Aluminum-rich metamorphic settings
Hydrothermal environments
- Occurs in veins and altered zones
It is often associated with:
- Gibbsite and boehmite
- Corundum
- Clay minerals
Common Locations
Notable occurrences of Diaspore include:
- Turkey: Major source of gem-quality material (Zultanite trade name)
- Russia: Ural Mountains
- China: Bauxite deposits
- United States: Arkansas and other regions
- Greece: Aluminum-rich deposits
Turkey is particularly известна for transparent, color-changing specimens.
Uses and Practical Significance
Diaspore has several uses:
Aluminum ore
- Part of bauxite, though less important than gibbsite in many deposits
Gemstone
- Transparent varieties are cut and sold (e.g., Zultanite)
- Known for color change under different lighting
Collecting
- Valued for well-formed crystals and gem material
Similar and Related Minerals
Diaspore may be confused with:
- Boehmite: Similar composition but typically softer and different structure
- Gibbsite: Softer and more earthy
- Corundum: Much harder (Mohs 9) and lacks cleavage
Distinguishing features include:
- Perfect cleavage
- Moderate to high hardness
- Occurrence in bauxite or metamorphic environments
Identification Notes for Collectors
- Look for bladed or tabular crystals with perfect cleavage
- Check hardness (6.5–7) and pearly cleavage surfaces
- Note association with bauxite minerals or corundum
- Observe possible color change in gem-quality material
- Use testing to distinguish from boehmite and gibbsite
Diaspore is an aluminum oxide-hydroxide mineral, recognized for its perfect cleavage, occurrence in bauxite deposits, and occasional use as a color-changing gemstone.