Polka Dot Agate or PDA is an orbicular agate popular for jewelry found a short drive past Madras, Oregon. That’s the headline attraction at the mine, but this site produces so much more. The mine recently changed ownership and reportedly was being considered for closure until a highly productive thunder egg bed was unearthed. Now, what’s being called the Canyon Rim bed is a popular attraction suitable for families and all ages.

The pictures above show some of the wild variety found in the Canyon Rim bed. These were found under an iron-heavy volcanic ash layer. The eggs at this site produce beautiful and delicate stalactites – some druzy (frosty and sparkly), some glassy, others contorted in otherworldly needle-like structures. A single egg can contain agate, jasper, aragonite, hematite, manganese, and common opal in a variety of colors and configurations.

Everything on this page was found in a roughly 10-foot radius at the site. The pit is that dense with material!

The rock pictured at right is ugly, but it shows some interesting developmental stages of a thunder egg at the PDA site. Look closely and you’ll see those ugly rough bits in the middle are actually needle-like filaments encased in a clear, glassy agate coating. They’re micro-stalactites! Inside a different volcanic bubble, those needles might have formed something more like the agate “angel finger” tubes at top right of this page. The heavy manganese and iron content likely shaped how it grew. If the bubble continued to fill in all the way with agate, it might have formed something more solid and mossy that could be cut into interesting patterned slabs. Instead, it’s an ugly somewhat intermediate rock that lets you wonder how exactly it formed like that.