Bone Opal

Bone opal, also called opalized bone, is fossilized bone in which the original bony material has been replaced or infilled by opal, a hydrated form of silica. The result preserves bone structure such as the porous internal texture while taking on opaline qualities.

Most bone opal is common opal in pale, bony tones, but rare specimens contain precious opal with play-of-color, making them prized fossils. Australia, particularly the Lightning Ridge and Coober Pedy regions, is famous for opalized vertebrate remains.

These fossils are scientifically significant and can be extremely valuable when they combine recognizable anatomy with vivid opal color.

Bone opal forms when buried bones are bathed in silica-rich groundwater. As organic material breaks down and porous bone tissue creates open spaces, dissolved silica precipitates into and replaces the structure.

When the silica deposits as ordered microspheres, the bone becomes precious opal with play-of-color; irregular deposition forms common opal. In Australia's opal fields, deeply weathered sedimentary basins provided both the silica and the long, low-temperature conditions needed.

The process can preserve fine bone microstructure, which is why opalized bones are valuable both as gems and as paleontological specimens.

Look for opal that preserves recognizable bone structure, such as spongy internal texture, joint shapes, or bone outlines, combined with opal traits: hardness about 5.5-6.5, vitreous to waxy luster, white streak.

Distinguish bone opal from opalized wood by its bone anatomy (porous, cellular bone texture) versus wood grain and rings. Precious bone opal shows play-of-color; common bone opal does not.

Beware of resin casts or reconstructed pieces sold as opalized bone. Genuine specimens show natural bone structure and the physical properties of opal, and high-water material may craze as it dries.

Bone opal is collected primarily as fossil specimens, and pieces showing both clear bone structure and play-of-color can be exceptionally valuable to collectors and museums. Some stable material is cut and set as unusual jewelry.

Scientifically, opalized bone is important for paleontology, occasionally preserving the remains of ancient reptiles and other vertebrates. Care must be taken to protect specimens from drying and impact.

Metaphysically, opal in general is associated with transformation and inspiration; opalized bone is sometimes given added symbolism, a traditional rather than scientific use.