It is nearly impossible to undertake a research project in high-pressure/temperature mineralogy without drawing on the ingenious and imaginative work of John C. Jamieson. Inventor and builder of several devices for making in situ X ray diffraction studies of samples at high pressure and temperature. John laid the ground work for some of the most exciting and productive years of research in experimental mineralogy. Using his devices, he found and described numerous high-pressure phases in important materials. In addition, he conducted experiments in shock-produced high-pressure phases and made ultrasonic measurements on the elasticity of geophysically important minerals. In recent years he recognized the great potential of synchrotron radiation and contributed very significantly to its development as a tool in mineral physics.