Terrigen crystals are crystals which have been shown to reveal Inhuman powers. If the crystal is destroyed, such as by being dropped, it will release Terrigen Mist. If someone with the right genetic markers is exposed to the mist, they will be enveloped in a stone-like cocoon. The cocoon will break away within a few minutes, to reveal the new Inhuman. Depending on their powers, their physical appearance may be radically changed, such as Gordon, who lost his eyes to the mist, but gained the ability to teleport great distances or Raina, who had thorn-like growths all over her face and hands, but gained the ability to see glimpses of the future.
If anyone else is exposed to the mist, and they are not destined to be Inhuman, they will simply start to turn to stone completely and become statues. This kills the affected person. Examples of non-Inhumans who have been killed by Terrigen Mist are Trip, and Robert Gonzales.
Sometimes, an Inhuman can come through the metamorphisis process looking as they always have. Examples of such Inhumans are Daisy Johnson, who developed seismic powers and control over vibration frequencies, Lincoln Campbell, who gained the ability to shoot electricity from his body, or Joey Gutierrez, who became able to melt metals at distances.