Geospeedometer (IMAGE) Vanderbilt University Caption Millimeter-sized quartz crystals like this, which formed in molten magma, are the basis of the geospeedometer. The black dots are blebs of molten rock captured in the crystal when it formed. Credit Gualda Lab, Vanderbilt University Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.