John Stockwell

The Formation of Thundereggs

  • DINNER MEETING - Tuesday, December 16, 2003
  • Location: Stanford University

  • 5:30 PM-Wine Tasting: . . . Mitchell Bldg., first floor
  • 6:15 PM-Dinner: . . . Mitchell Bldg., first floor
  • 7:30 PM-Meeting: . . . Bloch Lecture Hall (TCSEQ Room 201)

    see Map showing Mitchell
    Map showing Bloch

    Anyone wishing to attend the lecture only is welcome at no cost.

    This will be the 358th meeting since 1954.

    close-up photo of thunderegg
    Thunderegg. (Image from The Geode Kid


    Reflecting a widespread bias toward "rockhounds" and in contrast to the situation in Europe toward agate and other "cryptocrystalline" quartz as minerals, in the United States few geologists have taken an interest in the origin and formation of thundereggs. Yet these objects, by other names, were being commented upon in this country as early as 1893 and in Europe in the 18th century. The development of thundereggs is a complex process, distinctly different from the process that forms amygdaloidal nodules. Thundereggs occur, presumably worldwide, in acid volcanics and often display great beauty in cross section. Much work on their formation has been done in recent decades in Germany. Some experimental results have been achieved. A good paper by Daniel Kile, a USGS geologist in Denver, was published in 2002. Perhaps of most interest is a 385-plus-page study by the "Geode Kid" ( based on his very extensive observations while mining thundereggs in a variety of localities throughout the western U.S.

    About the Speaker

    head-and-shoulders photo of John Stockwell
    John Stockwell

    John Stockwell received his B.S. in geology magna cum laude at Yale in 1957. He was employed as an exploration geologist by BP Alaska and later Sohio from 1974 to 1981, working mainly on and in Alaska. After 1981 he remained in the Bay Area and eventually retired in 2002 from teaching high school earth science and chemistry. He now considers himself an amateur geologist who happens to have had some formal training and professional experience. He is a member of the board (K-12 programs) of the Northern California Geological Society, past president of North Bay Field Trips, and is currently Field Trips North chairperson for the California Federation of Mineralogical Societies. The past 10 years he has taken a considerable interest in thundereggs, collecting extensively and reviewing problems of their formation. These studies have led to a developing interest in acid volcanics. Mr. Stockwell resides in Berkeley.

    Reservations: The preferred way to make reservations is simply to email Janice Sellers at by Friday, December 12, tell her you will attend, commit to pay, and bring your payment to the meeting. Janice always emails a confirmation; if you don't get one, assume email crashed yet again and email her a second time. A check made to "PGS" is preferred, payable at the meeting.

    If you want to pay in advance:

    Stanford faculty and students: Please make dinner reservations by Friday, December 12. Contact Dr. Juhn Liou via his mailbox (and leave check), Geological and Environmental Sciences Office, Geocorner - Bldg. 320 (Rm. 118). Make checks out to "PGS."

    All others, including faculty and students from other Bay Area universities and colleges and USGS: Please make dinner reservations by Friday, December 12. Contact Janice Sellers, at Seismological Society of America, 201 Plaza Professional Building, El Cerrito, CA 94530, phone (510) 559-1780. Send check made out to "PGS" to Janice.

    Dinner is $30.00. Includes wine (5:30 to 6:15 PM.), dinner (6:15-7:30 PM.), tax, and tip.

    For students. We are happy to report that it looks like we are about to get our funding reinstated by Stanford to help pay for student dinners. Meanwhile, PGS can draw down the treasury and start now. The price is now back to $5 for students from any school; no-shows pay full price.

    Dues for Academic Year 2003-2004 ($10.00) should be sent to Janice Sellers, Seismological Society of America, 201 Plaza Professional Building, El Cerrito, CA 94530. Janice's phone: (510) 559-1780.

    Officers: Cheryl Smith, President; Mike Diggles, Vice President; Vicki Langenheim, Secretary; Janice Sellers, Treasurer; Adina Paytan, Field-Trip Czarina

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    Date created: 11/12/2003
    Last modified: 12/04/2003
    Created by: Mike Diggles, Vice President, PGS.
    c/o U.S. Geological Survey, MS-951, 345 Middlefield Road, Menlo Park, CA 94025. (650) 329-5404. email Mike Diggles at

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