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, 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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How much is agatized limb casts worth?+
What rocks look like 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.
