NAGT Rock and Mineral Exchange - Desired https://nagt.org/nagt/teaching_resources/exchange/index.html Quartz geode pieces needed https://nagt.org/nagt/teaching_resources/exchange/postings/183881.html Wed, 05 Jul 2017 00:00:00 -0500 https://nagt.org/nagt/teaching_resources/exchange/postings/183881.html Precambrian chert. Stromatolites. https://nagt.org/nagt/teaching_resources/exchange/postings/169280.html Tue, 03 Jan 2017 00:00:00 -0600 https://nagt.org/nagt/teaching_resources/exchange/postings/169280.html