White Opal Identification Guide
Identifying white (milky) opal by its light body tone, play-of-color, low density, and softness, versus moonstone and opalite.
Read the full White Opal encyclopedia entry →
What White Opal Looks Like
White opal — also called milky opal — is hydrated silica (SiO2·nH2O) with a light or white body tone. Precious white opal shows play-of-color: patches of spectral red, orange, green, and blue that flash and shift as the stone is moved, set against a pale milky background. Common (potch) white opal lacks this fire and appears uniformly milky. Luster is vitreous to waxy or resinous, and the stone is translucent to opaque with no crystal structure (opal is amorphous).
Key Visual Cues
- Pale/white body with moving spectral color flashes (precious type)
- Milky, slightly waxy or glassy luster
- No crystal faces; smooth conchoidal fracture
- Light in the hand for its size
Step-by-Step Field ID Checklist
- Tilt for play-of-color. Genuine precious opal flashes multiple spectral colors that move with the angle.
- Judge body tone. White opal has a light, milky ground (as opposed to black opal).
- Test hardness. Opal is soft and scratches with a steel point.
- Heft it. Opal feels notably light (low density).
- Check for crazing. Fine drying cracks are common in natural opal.
Diagnostic Tests
- Mohs hardness: 5.5–6.5 — softer than quartz; steel can scratch it.
- Streak: White.
- Cleavage/fracture: None; conchoidal fracture.
- Density: ~1.9–2.2 g/cm³ — light.
- Acid: Inert to dilute HCl.
Common Look-Alikes and How to Tell Them Apart
- Moonstone (feldspar): Shows a single billowy blue-white sheen (adularescence), not multiple spectral flashes, and has cleavage and higher density.
- Opalite (glass): Manufactured; a milky single-color glow with bubbles and no true play-of-color.
- Chalcedony / white agate: Harder (Mohs 7), denser, waxy, and shows no fire.
- Common opal (potch): Same mineral but no play-of-color; far less valuable.
- Doublets/triplets: Assembled stones show a flat color layer with a straight join line visible from the side; solid opal's color is three-dimensional throughout.
Where White Opal Is Found
White opal is the classic Australian opal type, mined chiefly at Coober Pedy and Andamooka (South Australia) and White Cliffs (NSW), where it fills cracks and replaces fossils in weathered Cretaceous sediments. It also occurs in Ethiopia, Brazil, and Mexico. Rockhounds search opal dirt and seams under strong, angled light.
Collecting Tips
Wet pale nodules and tilt them under bright directional light to reveal color flashes. Watch the edges for a straight glue line that would betray a doublet or triplet. Because opal is soft and can craze as it dries, keep finds stable and avoid sudden drying.
Frequently asked questions
How can you tell if white opal is real?
Real white opal shows play-of-color that shifts with the viewing angle, is light in weight, is soft (Mohs 5.5–6.5), and has a conchoidal fracture with no crystal faces. A straight join line at the edge indicates an assembled doublet or triplet.
What does white opal look like?
It has a milky, light-colored body with flashes of spectral red, green, blue, and orange (in precious opal) that move as you tilt it; common white opal is uniformly milky without the flashes.
White opal vs moonstone — what's the difference?
Moonstone shows a single blue-white floating sheen (adularescence) and has feldspar cleavage, while white opal flashes multiple spectral colors and is softer and lighter with no cleavage.
Is white opal the same as common opal?
Not exactly — white opal can be precious (with play-of-color) or common (potch, without it). Common white opal is the milky variety that lacks the spectral fire.
White Opal identified by the community
Recent White Opal specimens identified with Rock Identifier.
