Ice Opal Identification Guide
How to identify ice opal, the colorless, glassy, ice-like common opal, and tell it from girasol opal, quartz, and glass.
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What Ice Opal Looks Like
Ice opal is a colorless to faintly translucent variety of common opal (hydrated silica) prized for its clear, frosty, ice-like appearance. Many specimens lack play-of-color, while some show a faint internal glow (girasol effect):
- Color: colorless, water-white, or very pale; sometimes a faint bluish or milky cast
- Luster: vitreous, glassy and wet-looking
- Transparency: transparent to translucent, like a chip of ice
- Habit: massive nodules, seams, and rounded masses; no crystals
Step-by-Step Field ID Checklist
- Confirm the icy clarity. A clear, glassy, slightly frosted stone is the first clue.
- Check for play-of-color or sheen. Ice opal may be plain or show a soft floating light (girasol); flashing rainbow color means precious opal instead.
- Test hardness. Mohs 5.5–6.5; it is scratched by quartz and a steel file.
- Look for conchoidal fracture and no cleavage.
- Feel the weight. It is light for its size due to low density.
Key Diagnostic Tests
- Hardness: 5.5–6.5; softer than quartz (7), which is the key separator from rock crystal.
- Streak: white.
- Fracture: conchoidal; no cleavage.
- Density: low, ~1.9–2.2 g/cm3.
- No acid reaction.
- UV: may show a faint greenish or whitish fluorescence.
Common Look-Alikes
- Clear quartz (rock crystal): harder (7), forms hexagonal crystals with points, and is denser; quartz will scratch ice opal.
- Girasol quartz: a quartz with milky sheen; again harder than opal.
- Glass: can look identical but is harder, often has bubbles, and lacks opal's low density.
- Hyalite opal: botryoidal glassy crusts that glow bright green under UV; ice opal is massive and only faintly fluorescent.
- Hydrophane opal: absorbs water and changes clarity; ice opal is generally more stable.
- Cacholong/milk opal: more opaque, porcelain-white.
Where It Is Found
Ice opal is reported from volcanic opal fields including Mexico, Oregon and the western United States, Ethiopia, and Brazil, typically lining cavities and seams in volcanic host rocks alongside other common and precious opal.
Frequently asked questions
How can you tell if it's real ice opal?
Ice opal is colorless and glassy with an icy, slightly frosted look, has a hardness of only 5.5–6.5 (so quartz scratches it), shows conchoidal fracture, is light in the hand, and gives no acid reaction. Its softness versus quartz is the easiest confirmation.
What is the difference between ice opal and clear quartz?
Clear quartz is harder (7), denser, and grows as hexagonal crystals with points, while ice opal is softer (5.5–6.5), lighter, amorphous with conchoidal fracture, and never forms crystals.
What does ice opal look like?
It looks like a clear-to-translucent chip of ice or glass with a wet vitreous sheen, sometimes with a soft floating internal light, and usually little or no rainbow play-of-color.
Is ice opal the same as girasol opal?
They overlap. Ice opal that displays a soft bluish floating glow is often called girasol opal; plain colorless ice opal without that sheen is simply a clear common opal.