Three Minute Video on How Geodes Form

Here is a great video on how some agates form, perhaps most:

At this point, let me lapse into text from my now dead book project. This is me talking:

In the case of agates, some literature calls them a, “distinctly banded fibrous chalcedony.” While that may be true for science, a technical discussion on that beyond the scope of this book, agates are simply pretty, translucent at least in part, and common throughout America and the Southwest. I’ve described Burro Creek before. That’s an area in Arizona for collecting. The Cady Mountains in the Mojave Desert near Barstow, California has many kinds of agates, including what’s called the beautiful Top Notch. Clubs may have claims focused on agates, like the one near Las Vegas owned by the Southern Nevada Gem and Mineral Society.

In an interview with Valley Verde TV, Pat McMahan, the world’s leading agate expert, summed up their origin story in just a few unscripted sentences.

“An agate is actually a type of quartz. It’s a non-crystalline quartz and it often forms as a result of volcanic ash like what you have at Mount St. Helens. So, you have a lava flow like you have in Hawaii that has gas pockets and cracks in it — these become the future home of agates. You then have a subsequent eruption with volcanic ash. Rain falls on top of the ash, picking up the silica of the ash, ashes are a form of quartz, depositing that in the lava rock. The rain then soaks through the lava rock, fills the gas pockets, and if it picks up minerals in the process, you have agates that are colored and have inclusions of different kinds. More rain ensues, and ashes are washed away after millions of years, the lava rock turning into soil, with agates just laying there for us.”

Video with Pat explaining geode formation here:


In explaining petrified wood formation, Halka and Chronic use similar terms. “Because volcanic ash is made of tiny fragments of unstable silica glass, groundwater seeping through the sediments soon becomes charged with dissolved silica. The silica tends to come out of solution when it contacts organic material such as old wood or animal bones. Little by little it has accumulated in pore spaces within the trunks, bringing with it traces of iron, manganese, and other mineral substances that now add brilliant color to the wood.” If we can think of gas pockets and cracks filling with silica instead of replacing pore space within wood, we might better understand the process of agate building.

The first video graphically demonstrates what Halka and Chronic and I could only paint a picture of with words.
Follow me on Instagram: tgfarley

 Every Rock Has A Story YouTube Series for Kids - Please Share

 Every Rock Has A Story: A YouTube Series for Kids - please share


Dear Colleagues (with apologies for multiple posts),

I wanted to let you all know that my YouTube video series for kids called  “Every Rock Has A Story” is now complete.  Thanks again to the many friends and colleagues who sent good words and encouragement when I started making these videos in May.  The response from kids, parents, teachers, and the academic community has been overwhelmingly positive.  My YouTube channel now includes 44 original episodes plus a brand new Teacher-Parent Guide and accompanying teacher resources.  You can find it all here:
YouTube Channel
Teacher-Parent Guide
Link to my website with additional resources
While my target audience was grades K-4, the videos are fun and appropriate for all ages.  For the GSA membership, I might particularly suggest the messages in Episode #14, Episode #33, and Episode #43 if you’d like to take a peek yourself.  Watch a few episodes, have a laugh at my expense, and who knows, you might just discover a new perspective on rocks and minerals.  Afterall, we are all still learning.
Now, my principle aim is to get this educational resource into the hands of parents and teachers who might wish to incorporate it into Fall lesson planning and beyond. Communicating the value and excitement of science to young people has never been more important.  Given the positive response, I think that if more people knew about the videos more people would use them and benefit from them.  If you have any connections in your local school system, if you know any teachers or parents, please share this educational resource with them.  Tweet it, Facebook it, email it, text it, morse code it… whatever works.  I made the video series in an effort to help parents and teachers through the challenges of the COVID19 shutdown when many kids (including my own) were stuck learning from home.  Now, it is a lasting open resource that (I hope) can help inspire the next generation of geoscientists.
Thanks for sharing Every Rock Has A Story with kids, parents, and teachers you know.  I hope everyone is safe and well during this challenging time.