Iridescent ammonite is a rare, fossilized shell that displays vibrant, spectral play-of-color due to microscopic layers of aragonite. Collectors prize high-quality specimens for their intense, flashing rainbows, which are best observed when the surface is properly stabilized and polished. It is primarily sourced from the Bearpaw Formation in Alberta, Canada, where specific pressure and mineral conditions created this unique gemstone.
Is this iridescent ammonite?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch iridescent ammonite with a known reference. Iridescent Ammonite sits at Mohs 3.5-4 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Iridescent Ammonite leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Iridescent Ammonite typically shows a pearly luster.
- 4Match the color rangeCompare against the expected color range: iridescent, red, green, gold, blue, purple.
- 5Look at form & habitTypical habit: conchoidal fossilized shell.
Often confused with
Iridescent Ammonite vs. its common look-alikes — and how to tell them apart in the field.
How to tell apart: Labradorite is the harder of the two (Mohs 6-6.5 vs. 3.5-4); luster reads pearly on Iridescent Ammonite and vitreous on Labradorite.
How to tell apart: Opal is the harder of the two (Mohs 5.5-6.5 vs. 3.5-4); luster reads pearly on Iridescent Ammonite and vitreous on Opal.
Often found alongside iridescent ammonite
Minerals reported to co-occur with iridescent ammonite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 3.5-4
- Density
- 2.6-2.8 g/cm³
- Streak
- White
- Luster
- Pearly
- Transparency
- Opaque
- Crystal habit
- Conchoidal Fossilized Shell
- Cleavage
- None
- Rarity
- Rare
- Uses
- Gemstone, Collector, Jewelry
- Host rock
- Marine Sedimentary Shale
- Typical price
- $50-500 for small fragments, $1000+ for high-grade specimens
Where rockhounds find iridescent ammonite
Classic worldwide localities
- Alberta, Canada
- Madagascar
- United States
Field-hunting tip
Look in marine sedimentary shale country — that is the host setting where iridescent ammonite typically forms. If you start seeing calcite, pyrite, siderite in float, you are in the right ground. Field specimens usually show a conchoidal fossilized shell habit, so train your eye for that shape before scanning the outcrop.
Common questions
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Find iridescent ammonite on the map
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