Hyalite is a clear, colorless variety of opal often found as bubbly or botryoidal crusts inside volcanic rock geodes. Collectors prize it for its spectacular and intense green fluorescence under ultraviolet light, caused by trace amounts of uranyl ions. It is best displayed under shortwave UV light to observe its signature neon-green reaction.
Is this hyalite opal geode?
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 hyalite opal geode with a known reference. Hyalite Opal Geode sits at Mohs 5.5-6.5 — softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Hyalite Opal Geode leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Hyalite Opal Geode typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, yellow.
- 5Look at form & habitCrystal system: amorphous. Typical habit: botryoidal, crusts, globular.
Often confused with
Hyalite Opal Geode vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside hyalite opal geode
Minerals reported to co-occur with hyalite opal geode. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Chemical formula
- SiO₂·nH₂O
- Mohs hardness
- 5.5-6.5
- Density
- 2.0-2.1 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Transparent
- Crystal system
- Amorphous
- Crystal habit
- Botryoidal, Crusts, Globular
- Cleavage
- None
- Fluorescence
- Intense Bright Green Under SW and LW UV
- Rarity
- Uncommon
- Uses
- Collector, Decorative
- Host rock
- Volcanic Rhyolite Cavities
- Typical price
- $20-150 for thumbnail to cabinet specimens
Where rockhounds find hyalite opal geode
1 mapped spotsClassic worldwide localities
- Zacatecas, Mexico
- San Luis Potosí, Mexico
- Eureka, Utah, USA
- Frankfurt, Germany
- Karur, India
Field-hunting tip
Look in volcanic rhyolite cavities country — that is the host setting where hyalite opal geode typically forms. If you start seeing quartz, chalcedony, goethite in float, you are in the right ground. Field specimens usually show a botryoidal, crusts, globular habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in North Carolina — start trip planning there.
Common questions
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Find hyalite opal geode on the map
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