Hydrophane Opal Identification Guide
A field guide to hydrophane opal, the porous opal that turns transparent in water and sticks to your tongue, with safe testing tips.
Read the full Hydrophane Opal encyclopedia entry →
What Hydrophane Opal Looks Like
Hydrophane is a porous variety of opal (hydrated silica) that absorbs water, dramatically changing its appearance. Most Ethiopian Welo opal is hydrophane:
- Color: body color ranges from milky white and cream to amber, chocolate, and crystal-clear; precious hydrophane shows play-of-color
- Luster: vitreous to waxy
- Transparency: changes — opaque or cloudy when dry, becoming more transparent when wet
- Habit: massive nodules and seams; no crystals
Step-by-Step Field ID Checklist
- Observe the dry stone. Note its body color and any play-of-color.
- The tongue/stick test. Hydrophane is porous; a clean dry piece will lightly stick to a moistened tongue. (Use only on rough you own.)
- The water test. Place a drop of water on it. Hydrophane absorbs it, darkening and clarifying, and its play-of-color may temporarily fade or shift.
- Watch it dry. As it dries, transparency and color return — confirming hydrophane behavior.
- Test hardness gently. Mohs 5.5–6.5.
Key Diagnostic Tests
- Water absorption: the defining test. Hydrophane visibly drinks water and changes clarity and color, then reverts on drying.
- Hardness: 5.5–6.5; softer than quartz.
- Streak: white.
- Fracture: conchoidal; no cleavage.
- Density: low (~1.9–2.2 g/cm3), and it can feel lighter when fully dry.
- No acid reaction.
Caution: because it absorbs liquids, never clean hydrophane in water for long, and keep it away from oils and dyes, which it will also absorb and which are used to fake color.
Common Look-Alikes
- Non-hydrophane (Australian) opal: does not absorb water or stick to the tongue; stable play-of-color.
- Treated/dyed hydrophane: smoked or sugar-treated stones mimic black opal; uneven color concentrated in cracks is a warning sign.
- Common opal/opalite glass: opalite (man-made glass) is non-porous, will not stick to the tongue, and shows a blue sheen with orange transmitted light.
- Chalcedony: harder (7), non-porous, no water absorption.
Where It Is Found
The dominant source is the Wollo (Welo) Province of Ethiopia, with hydrophane also from the older Shewa (Mezezo) Ethiopian deposits. Hydrophane behavior is occasionally noted in opals from Mexico, Oregon, and other volcanic localities.
Frequently asked questions
How can you tell if it's real hydrophane opal?
Genuine hydrophane absorbs water: a drop placed on it soaks in, darkening and clarifying the stone, and it lightly sticks to a moistened tongue. The change reverses as the opal dries. Hardness is 5.5–6.5 with conchoidal fracture and no acid reaction.
Why does my opal change color or go clear when wet?
That is normal hydrophane behavior. The opal is porous and absorbs water, which raises its transparency and can temporarily mute or shift its play-of-color until it dries out and returns to normal.
What does hydrophane opal look like?
Dry, it looks like a milky, amber, or crystal opal, sometimes with flashes of play-of-color; wet, it becomes noticeably more transparent and darker, then reverts as it dries.
Can you get hydrophane opal wet?
Brief contact is fine and is how you test it, but prolonged soaking can cause cracking (crazing) or let dyes and oils stain it, so avoid water cleaning and keep it away from colored liquids.