Opalized Ammonite
What is Opalized Ammonite?
Opalized Ammonite is a fossil where the original shell of an ammonite, an extinct marine mollusk, has been replaced by opal. This process, known as opalization, occurs when the organic material of the shell dissolves and is replaced by silica-rich solutions. Over time, the silica hardens, forming opal while preserving the intricate details of the ammonite's shell. The resulting gemstone exhibits a play-of-color, displaying flashes of various colors due to the diffraction of light within the opal's structure. The appearance of Opalized Ammonites can vary widely, with some displaying vibrant, iridescent colors, while others may have a more subdued appearance. The quality and value of the gemstone depend on the intensity of the play-of-color, the clarity of the opal, and the preservation of the ammonite's fossil structure.
Optical Properties
- Refractive Index
- 1.44 - 1.46
- Birefringence
- None
- Pleochroism
- None
- Optical Character
- Isotropic
- Dispersion
- Moderate to strong
Market Value Factors
Pricing varies for every rock and mineral, so use these universal factors to gauge Opalized Ammonite before comparing listings or appraisals.
Size & Weight
Larger, intact specimens usually command higher prices.
Rarity & Demand
Scarce material or popular varieties sell at a premium.
Condition & Finish
Chips, repairs, and heavy wear lower value; clean prep helps.
Treatment & Provenance
Untreated specimens with documented locality are prized.
Opalized Ammonite Localities Map
See where Opalized Ammonite is found with a localities map, collecting zones, and geology context. Generate a sample map preview below.
Quick Facts
Physical Properties
- Color
- Displays a wide range of colors, including iridescent flashes of red, orange, yellow, green, blue, and violet. The base color can be white, gray, black, or other colors.
- Hardness (Mohs)
- 5.5 - 6.5
- Density
- 2.10 - 2.20 g/cm³
- Streak
- White
Chemical Properties
- Chemical Formula
- SiO2·nH2O
- Elements
- Silicon, Oxygen, Water (H2O), with trace elements depending on the specific opal and the fossil's composition.
Also Known As
Identify Opalized Ammonite Instantly
- Snap a photo, get instant results
- 6,700+ rocks, minerals & crystals
- Discover collecting spots near you
Opalized Ammonite FAQs
How do I identify Opalized Ammonite?
Opalized Ammonite can be identified by its hardness of 5.5 - 6.5 on the Mohs scale, Displays a wide range of colors color. Look for these key characteristics when examining specimens.
What color is Opalized Ammonite?
Opalized Ammonite typically appears in Displays a wide range of colors, including iridescent flashes of red, orange, yellow, green, blue, and violet. The base color can be white, gray, black, or other colors.. Color can vary depending on impurities and formation conditions.
How hard is Opalized Ammonite?
Opalized Ammonite has a hardness of 5.5 - 6.5 on the Mohs scale. This gives it moderate hardness.