Natural Black Opalized Wood 13.34ct Oval Cabochon

An elongated oval cabochon of opalized wood, cut from a piece of ancient timber whose cell structure has been replaced by silica. In white light the body reads as a deep brownish black under a high-gloss polish, and the original grain is still legible across the dome as fine parallel lines and a network of cellular texture. Tilted toward the light, small pinpoints of red, orange and violet play-of-color spark along the central band where the silica settled into an ordered structure, scattered rather than continuous, and all the brighter for sitting against so dark a background.

Play-of-color comes from light diffracting through microscopic silica spheres stacked in a regular grid. Where that grid formed cleanly, color appears; where it did not, the material stays dark. In opalized wood the two states sit side by side, and that contrast is exactly what gives this piece its character. Indonesia is a well-known source of opalized and silicified wood, much of it from Java and Sumatra, where volcanic ash buried standing forests. The stone is untreated. Opal sits around 5.5 to 6.5 on the Mohs scale and prefers gentle handling, so a pendant or a protected setting suits it better than daily knocks. At 36.6mm long it has the proportions for a bar pendant. Opal is the October birthstone.

Natural opalized wood, Indonesia, untreated, sold loose.