Aventurescence
Aventurescence in gemstones including sunstone and aventurine quartz with causes, types, and quality factors.
Introduction
Aventurescence is a glittery, metallic reflection from flat, reflective inclusions
within a gem. The effect is named after aventurine glass (from Italian "avventura"
meaning chance), which was discovered accidentally when copper filings fell into
molten glass.
The sparkle comes from light reflecting off platy inclusions—typically metallic
or reflective mineral flakes oriented within the host crystal.
Mechanism
How aventurescence forms:
Requirements
- Flat, platy, reflective inclusions
- Inclusions oriented parallel or sub-parallel
- Sufficient inclusion density for visible effect
- Transparent to translucent host material
Sunstone
Sunstone is feldspar with metallic schiller from oriented platelets:
Oregon Sunstone
Unique copper-bearing feldspar:
- Inclusions: Copper metal platelets
- Effect: Metallic orange-red to golden sparkle
- Colours: Colourless to green to red body
- Unique: Only copper sunstone in the world
- Varieties: Some transparent without schiller
Indian/Norwegian Sunstone
- Inclusions: Hematite or goethite platelets
- Effect: Red-brown metallic sparkle
- Character: Often more orange-brown
- Sources: India, Norway, Tanzania
Oregon Sunstone Features
| Feature | Description |
|---|---|
| Copper schiller | Distinct metallic sparkle |
| Bicolour | Green and red zoning |
| Tricolour | Multiple distinct colours |
| Transparent | Clear with no schiller |
| Dichroism | Strong colour variation |
Oregon Sunstone Uniqueness
Aventurine Quartz
Aventurine is quartz with platy inclusions creating sparkle:
Green Aventurine
The most common type:
- Inclusions: Fuchsite (chrome mica) flakes
- Colour: Green from the fuchsite
- Character: Translucent with sparkle
- Uses: Cabochons, carvings, beads
Other Colours
| Colour | Inclusions | Characteristics |
|---|---|---|
| Green | Fuchsite mica | Most common; chrome green |
| Orange-red | Hematite/goethite | Warmer colour |
| Blue | Dumortierite | Rare; often misidentified |
| Peach/pink | Mica + iron oxides | Less common |
Quality Factors
Assessing aventurescent gems:
| Factor | Premium Quality |
|---|---|
| Schiller intensity | Strong, visible sparkle |
| Schiller distribution | Even across stone |
| Body colour | Attractive (Oregon red valued) |
| Transparency | Translucent preferred for some |
| Inclusion quality | Clean platelets, not cloudy |
Aventurine Glass
The phenomenon's namesake:
History
- Discovered accidentally in Murano, Italy (~17th century)
- Copper filings fell into molten glass
- Created sparkly decorative glass
- Name transferred to natural materials
Identification
Distinguishing natural from glass aventurine:
- Glass may have more uniform sparkle
- Glass often shows gas bubbles
- Glass SG differs from quartz (2.5 vs 2.65)
- Glass often has different colour quality
Market Notes
Aventurescent gems in the market:
- Oregon sunstone: Premium for copper stones; collector interest
- Green aventurine: Common; affordable
- Sunstone general: Popular for unique effect
- Treatment: Not common; natural phenomenon
- Value: Determined by strength of effect and body colour