Joel A. Bartsch leads the Houston Museum of Natural Science (HMNS) as CEO and president. As the co-author of Masterpieces of the Mineral World: Treasures from the HMNS, Joel A. Bartsch highlights remarkable geologic discoveries from around the globe.
One of the most striking pieces in the HMNS Cullen Hall of Gems and Minerals is a 2,765-carat boulder opal. Shaped like a large egg with a flat base, the remarkable multi-hued piece was sourced in Australia, where many opal finds are made.
The development of opal takes millions of years, as water trickles down through sandstone and picks up silica along the way. This silicon dioxide and water solution ultimately fill voids and cracks around decomposing fossils or in faults in the rock. A vast majority of such opal deposition is known as “potch” by miners and is not considered precious, as there is minimal color and light interplay.
Unlike precious sedimentary opal, boulder opal is attached to the ironstone it forms around. These stones are typically cut by gemologists such that the ironstone backing remains intact. While these may be cut into standard shapes, they are also envisioned as freeform pieces that reflect the natural contours of the ironstone.
