An agatized limb cast forms when silica-rich fluid fills the empty mold left after a tree limb decays in volcanic ash. Collectors look for clearly defined bark-like texture or a cylindrical shape with detailed internal banding. It is sought after by lapidary artists for its intricate pattern and superior hardness.
Is this agatized limb cast?
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 cast with a known reference. Agatized Limb Cast 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 Cast leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Agatized Limb Cast 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 Cast vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside agatized limb cast
Minerals reported to co-occur with agatized limb cast. 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
Where rockhounds find agatized limb cast
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 cast 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 cast?+
Where is agatized limb cast found?+
Can I find agatized limb cast in the United States?+
What rocks look like agatized limb cast?+
What minerals are found with agatized limb cast?+
What kind of rock does agatized limb cast form in?+
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Find agatized limb cast on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
