Hyalite is a clear, colorless variety of opal often found as bubbly or globular botryoidal crusts. It is most famous among collectors for its spectacular, intense neon-green fluorescence under ultraviolet light, which is caused by trace amounts of uranium impurities. It typically forms as a coating on rocks within volcanic environments or pegmatites.
Is this hyalite?
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 with a known reference. Hyalite 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 leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Hyalite typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: colorless, white, yellowish, greenish.
- 5Look at form & habitCrystal system: amorphous. Typical habit: botryoidal, crusts, globular, stalactitic.
Often confused with
Hyalite vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside hyalite
Minerals reported to co-occur with hyalite. 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, Stalactitic
- Cleavage
- None
- Fluorescence
- Intense Bright Green Under SW and LW UV
- Rarity
- Common
- Uses
- Collector, Specimen
- Host rock
- Volcanic Rhyolite, Pegmatites, Hydrothermal Cavities
- Typical price
- $10-100 per specimen
Where rockhounds find hyalite
2 mapped spotsClassic worldwide localities
- Zacatecas, Mexico
- San Luis Potosi, Mexico
- Karlovarský, Czech Republic
- Georgia, USA
- North Carolina, USA
Field-hunting tip
Look in volcanic rhyolite, pegmatites, hydrothermal cavities country — that is the host setting where hyalite typically forms. If you start seeing quartz, topaz, cassiterite in float, you are in the right ground. Field specimens usually show a botryoidal, crusts, globular, stalactitic habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Utah — start trip planning there.
Common questions
How do you identify hyalite?+
Where is hyalite found?+
Can I find hyalite in the United States?+
How much is hyalite worth?+
What rocks look like hyalite?+
What minerals are found with hyalite?+
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Find hyalite on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
