Where Can You Find Agate Stones Forming?

Question

I'm fascinated by agate, especially the kind found in basaltic or other lava cavities.  The stones from Botswana and Brazil are my favorites.  These were formed at some time in the remote past. After the lava had hardened, water solutions went to work in the gas cavities.  The little (and sometimes not so little) precious stones were created layer by layer.

I was wondering if anyone knows where this process is currently taking place. After all, volcanic eruptions aren't confined to the distant past. The conditions for agate nodule production must be present somewhere in the world where lava has flowed relatively recently.  Has anyone heard of agate being found forming in places like Yellowstone or around Mount St. Helens?

Norm Gotch

Answer

I frequently travel to Iceland.  I've seen small samples of hardened lava with cavities filled with agatized deposits. I've also found a few basaltic specimens that had quartz crystals filling in the voids in the matrix.

I've only encountered voids with pea-sized agate deposits. I have seen dyed specimens in souvenir shops on occasion. The black lava doesn't show the dye, but the small agate stones are frequently light blue and almost opalescent.

Bob Wahlberg

Editor's Note: Check out these photos of agate from Iceland taken by Colin MacDiarmid in 2011.