Freeze-dried ice cream looks like the original product, and even tastes pretty good, but "drying" ice cream at room temperature would leave a sour-smelling, sloppy mess. Similarly, diamonds ejected from deep in the Earth can survive the journey intact only if they head toward the surface quickly and under just the right conditions.
Diamonds, found almost exclusively within kimberlite formations, are stable at great depth and at the planet's surface but rapidly turn to graphite under the high temperature/low pressure condi-tions of most eruptions.