NAGT Rock and Mineral Exchange - Desired https://nagt.org/nagt/teaching_resources/exchange/index.html #50States50Rocks https://nagt.org/nagt/teaching_resources/exchange/postings/197184.html Fri, 12 Jan 2018 00:00:00 -0600 https://nagt.org/nagt/teaching_resources/exchange/postings/197184.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