White Cliffs Opal Identification Guide

What White Cliffs Opal Looks Like

White Cliffs opal is precious and common opal from the historic White Cliffs field in New South Wales, Australia. It is hydrated silica (SiO2·nH2O). Precious specimens have a light or white body tone with flashes of play-of-color — patches of spectral red, green, blue, and gold that shift as the stone is tilted. The luster is vitreous to waxy or resinous, and transparency ranges from translucent to opaque. White Cliffs is especially famous for "pineapples" — opal pseudomorphs after crystal clusters (originally ikaite/glauberite) that form spiky, branching shapes.

Key Visual Cues

• Pale or white body color with moving spectral flashes (in precious opal)
• Waxy to glassy luster
• Occasional spiky pseudomorph ("pineapple") forms unique to this field
• No crystal faces — opal is amorphous

Step-by-Step Field ID Checklist

1. Tilt for play-of-color. Rotate the stone under light; true precious opal flashes shifting spectral colors, not a single static sheen.
2. Assess body tone. White Cliffs material is typically light/white-bodied rather than black.
3. Check hardness. Opal is relatively soft and scratches with a steel point.
4. Heft it. Opal feels light for its size (low density).
5. Look at the form. A spiky pseudomorph is a strong White Cliffs signature.

Diagnostic Tests

• Mohs hardness: 5.5–6.5 — softer than quartz; a knife or hardened steel can scratch it.
• Streak: White.
• Cleavage/fracture: No cleavage; conchoidal fracture.
• Density: ~1.9–2.2 g/cm³ — noticeably light.
• Acid: Inert to dilute HCl.

Common Look-Alikes and How to Tell Them Apart

• Other white/light opal (Coober Pedy, Andamooka): Mineralogically identical; locality is inferred from provenance, body tone, and the distinctive pineapple pseudomorphs unique to White Cliffs.
• Opalite / opalized glass: Man-made glass shows a milky single-color glow (adularescence-like), bubbles, and no true play-of-color.
• Moonstone: Feldspar with a blue-white billowy sheen (adularescence) but no spectral color flashes; it is harder (Mohs 6–6.5) and has cleavage.
• Chalcedony / white agate: Harder (Mohs 7), denser, and shows no play-of-color.
• Common (potch) opal: Same field, but lacks play-of-color; valued far less.

Where White Cliffs Opal Is Found

White Cliffs lies in far-western New South Wales and was one of Australia's earliest commercial opal fields (from the 1880s). Opal occurs in weathered Cretaceous sedimentary rocks, filling cracks and replacing fossils and crystals. The field is the type locality for opal pineapples.

Collecting Tips

Examine pale nodules and seams under strong directional light, tilting to catch color flashes. Because opal is soft and can craze (crack) as it dries, handle field finds gently and keep them stable. Genuine play-of-color that moves with the viewing angle is the definitive sign of precious opal.