AI is spot on — that's black opal. The play-of-colour looks like a rolling flame pattern. If you're near Level 4 shaft, I've been pulling similar stones from that seam all month.
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AI Confidence
94%
Collector Value Rating
4.8 / 5.0
Common rock
Semi-precious
Precious
Rare gem
Exceptional · Among the world's most valuable gem materials per carat
Black Opal
Precious opal · N2 body tone · Hydrated silica (SiO₂·nH₂O)
Est. value: $1,200 – $2,400 AUD
Mineral groupMineraloid (amorphous silica)
FormulaSiO₂·nH₂O
Hardness (Mohs)5.5 – 6.5
LustreVitreous to resinous
FormationArtesian basin sediment replacement over 100M+ years
Care note6–10% water content — avoid extreme temperature changes
Key value factorPlay-of-colour, pattern, body tone (N1–N4)
Top benchmarkHarlequin N1 = $5,000–$15,000/ct
Est. gradeN2, rolling flame pattern
Best marketsJapan, USA, UAE
TreatmentNone detectable
In Ancient Rome, opal was considered the most precious of all gems, symbolising hope and purity. The Aboriginal people of Lightning Ridge regard opals as sacred — gifts left by the Rainbow Serpent as it moved through the earth.
October's birthstone. In the Middle Ages it was said to grant the wearer invisibility when wrapped in a fresh bay leaf.
Primary sourceLightning Ridge & White Cliffs, NSW — 90% of world black opal
Secondary (AU)Coober Pedy SA · Mintabie SA · Quilpie QLD
InternationalWelo Ethiopia · Querétaro Mexico · Virgin Valley Nevada
RarityRarest form of precious opal. N1 grades exceptionally scarce.
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O
G
I'd call it N2. Wet the stone and check if the play-of-colour holds — yours looks solid. Worth getting a weight on it before you list.