Priday Plume Agate

Priday plume agate is a famous plume agate from the Priday Ranch (Priday Agate Beds) area near Madras in central Oregon. It is celebrated among collectors for delicate, feather-like mineral plumes of red, gold, brown and black suspended within a translucent grey to colorless chalcedony.

The material occurs largely inside thundereggs, the rounded nodules that weather out of Oregon's volcanic rhyolite. When sawn and polished, the plumes appear to float in three dimensions inside the clear stone, creating miniature scenes.

Its long history, excellent lapidary quality and scenic plumes make Priday a benchmark name in American agate collecting.

Priday plume agate formed in gas cavities and thundereggs within rhyolitic volcanic ash and lava flows of central Oregon. Silica-rich groundwater filled these cavities and deposited chalcedony as the host rock cooled and altered.

While the silica was still a soft gel, iron- and manganese-bearing solutions seeped in and crystallized as three-dimensional, branching plumes and mossy growths. The surrounding silica then hardened around them, locking the feathery plumes in place.

Thundereggs began as gas pockets in rhyolite; silica and other minerals later filled the star-shaped cavities. Weathering frees the nodules from the soft volcanic matrix at the Priday beds, where rockhounds have collected them for generations.

Look for translucent grey to clear chalcedony containing soft, feathery, three-dimensional plumes in red, gold, brown or black; the floating plume effect is the key trait. Many pieces come from thunderegg nodules with a rhyolite rind.

Hardness is 6.5-7, with a waxy to vitreous luster, white streak and conchoidal fracture.

Look-alikes: moss agate has flatter, greener, more tangled inclusions; dendritic agate shows two-dimensional fern-like dendrites rather than rounded plumes; sagenite agate has needle-like sprays instead of soft feathers. The three-dimensional, billowy plume habit and Oregon thunderegg matrix point to Priday.

Priday plume agate is a premier cabbing and collecting material, cut into cabochons, slabs and display pieces that showcase the floating plumes. Scenic specimens are highly sought after and can command strong prices.

It polishes beautifully and is durable enough for pendants, rings and bolo ties. Whole and half thundereggs are also popular as natural display specimens.

Metaphysically, plume agates are linked to growth, vitality and connection with nature, though such associations are traditional rather than scientific.