Agatized limb casts are fossilized remains formed when silica-rich fluids filled the empty molds left behind after tree limbs decayed in volcanic ash. Collectors look for clearly defined bark-like textures or cylindrical shapes with detailed internal banding. They are highly sought after by lapidary artists for their intricate patterns and superior hardness.
Is this agatized limb casts?
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 agatized limb casts with a known reference. Agatized Limb Casts sits at Mohs 6.5-7 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Agatized Limb Casts leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Agatized Limb Casts typically shows a waxy luster.
- 4Match the color rangeCompare against the expected color range: brown, red, yellow, white, gray, black.
- 5Look at form & habitCrystal system: trigonal. Typical habit: botryoidal.
Often confused with
Agatized Limb Casts vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside agatized limb casts
Minerals reported to co-occur with agatized limb casts. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- SiO₂
- Mohs hardness
- 6.5-7
- Density
- 2.55-2.65 g/cm³
- Streak
- White
- Luster
- Waxy
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Botryoidal
- Cleavage
- None
- Rarity
- Uncommon
- Uses
- Lapidary, Collector, Decorative
- Host rock
- Volcanic Ash Deposits
- Typical price
- $10-100 per specimen depending on quality and size
Where rockhounds find agatized limb casts
1 mapped spotsClassic worldwide localities
- Oregon
- Washington
- Arizona
- Idaho
- Nevada
Field-hunting tip
Look in volcanic ash deposits country — that is the host setting where agatized limb casts typically forms. If you start seeing quartz, calcite, opal in float, you are in the right ground. Field specimens usually show a botryoidal habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Oregon — start trip planning there.
Common questions
How do you identify agatized limb casts?+
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Can I find agatized limb casts in the United States?+
How much is agatized limb casts worth?+
What rocks look like agatized limb casts?+
What minerals are found with agatized limb casts?+
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Find agatized limb casts on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
