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UNDERSTANDING ORB STRUCTURE IN JASPERS

Manifestations of an Enigmatic Phenomenon (Part I)
Detailed view of orbs in a specimen of Morrisonite jasper.

The “orb” or egg shape in porcelain jaspers is highly sought after by collectors for the elegant patterns it creates in these fine-grained jaspers. These features are also intriguing because they are rare and because the origin of their formation remains a mystery. Figure 1 shows four examples of orb structure from four important deposits – Bruneau Jasper, Blue Mountain Jasper, Morrisonite Jasper, and Royal Imperial Jasper. Each contains a central circular or elliptical feature against a background of replicas. These approximately round features are widely known as orbs or orbicular structures. These examples were chosen because they provide the clearest illustrations of the most recognizable forms of the phenomenon. Orb structure is often manifested in more complicated forms along with other associated structures, which will be illustrated and discussed in Part 2 of this two-part series of articles.

The best-known jaspers in which to find this type of orb structure are: Bruneau Jasper (Bruneau Canyon, Idaho), Blue Mountain Jasper (McDermitt, Oregon), Carrasite Jasper (Rocky Canyon, Oregon), Misty Mountain/Polychrome Jasper (Madagascar), Morrisonite Jasper (Morrison Ranch, Oregon), Royal Imperial Jasper (San Cristobal, Zacatecas, Mexico), and Willow Creek Jasper (Eagle, Idaho). This list is not exhaustive. Indeed, orbs are a general aspect of jasper genesis and can occur whenever the proper conditions exist.

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About Rock&Gem Magazine

Rock & Gem June 2019, Jasper Orbs : Formation of Unique Features, Turquoise Mining, Special Section : Tools of the Trade, And More...