Feathers & Fingerprints

Feathers and fingerprints are healed or partially healed fractures within gemstones.
These features form when fractures that developed during or after crystal growth
are subsequently healed by circulating fluids, leaving characteristic patterns.

Feathers are internal fractures that have a wispy, feathery appearance:

Characteristics:

• Appear as wispy, irregular planes
• May show iridescence from thin-film interference
• Can affect durability if reaching surface
• Common term used in diamond grading

Formation:

• Stress during crystal growth
• Post-formation stress or shock
• Partial healing may occur

Fingerprint inclusions are healed fractures with characteristic patterns:

Appearance:

• Networks of tiny fluid remnants
• Pattern resembles human fingerprints
• Often show maze-like or net-like design
• May contain scattered droplets

Formation process:

1. Fracture develops in crystal
2. Fluids enter the fracture
3. Crystal partially heals around fluid
4. Trapped fluid forms fingerprint pattern

Liquid feathers are partially healed fractures still containing significant fluid:

Characteristics:

• Feather-like fracture outline
• Visible fluid within the fracture
• May contain gas bubbles
• Can show movement when tilted

Common in:

• Spessartine garnet (very characteristic)
• Some tourmalines
• Various other gems

Stress fractures form around included crystals due to differential expansion:

Formation:

• Included crystal has different thermal expansion
• Temperature changes create stress
• Fractures radiate from inclusion

Examples:

• Zircon halos in corundum and other gems
• Tension cracks around garnet inclusions
• Discoid fractures (lily pads) around chromite in peridot

Lily pad inclusions are diagnostic for peridot:

Description:

• Flat, disc-shaped stress fractures
• Radiate from a central crystal inclusion
• Resemble lily pads on a pond
• Usually surrounding chromite crystals

Diagnostic value:

• Virtually diagnostic for peridot
• Confirms natural origin
• One of most distinctive inclusion types

To observe feathers and fingerprints effectively:

Lighting:

• Darkfield - Best for seeing feathers as bright features
• Fibre-optic - Pinpoint illumination for detail
• Reflected light - Shows surface-reaching fractures

Method:

1. Start with low magnification for overview
2. Increase magnification for pattern detail
3. Rotate stone to see full extent of feature
4. Note whether feature reaches surface