Hyalite is a transparent, colorless variety of opal that typically forms botryoidal crusts or glassy, globular aggregates. It is most famous among collectors for its spectacular, intense neon-green fluorescence caused by uranyl ion inclusions, making it a favorite for display under UV lighting.
Is this hyalite opal?
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 with a known reference. Hyalite Opal 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. Streak: white.
- 3Read the lusterHold the specimen under a strong light. Luster: vitreous.
- 4Match the color rangeCompare against the expected color range: colorless, white, yellowish.
- 5Look at form & habitCrystal system: amorphous. Typical habit: botryoidal, crusts, globular, stalactitic.
Often confused with
Hyalite Opal vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside hyalite opal
Minerals reported to co-occur with hyalite opal. 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
- 2.0-2.2 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
- Uncommon
- Uses
- Collector, Lapidary
- Host rock
- volcanic cavities, hydrothermal veins
Where rockhounds find hyalite opal
7 mapped spotsClassic worldwide localities
- Mexico
- Czech Republic
- USA
- Hungary
- Germany
Field-hunting tip
Where it forms: volcanic cavities, hydrothermal veins. If you start seeing quartz, calcite, zeolites in float, you are in the right ground. Typical habit: botryoidal, crusts, globular, stalactitic. Train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in North Carolina, Maryland, Montana. Start trip planning there.
More hyalite opal photos
Common questions
How do you identify hyalite opal?+
Where is hyalite opal found?+
Can I find hyalite opal in the United States?+
What rocks look like hyalite opal?+
What minerals are found with hyalite opal?+
What kind of rock does hyalite opal form in?+
What is hyalite opal used for?+
Find hyalite opal on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
