Trigons on a diamond from the Fort a la Corne deposit in Saskatchewan, Canada. Image by Janina Czas / University of Alberta.
Trigons are one of the most common surface features on a rough natural diamond, and form during dissolution by fluids in the mantle and kimberlite.
Left alone without dissolution, diamond will remain a perfect octahedron or a cube. But with dissolution, diamond can change from an octahedron to other forms such as dodecahedroid or tetrahexahedroid (THH), and even form “irregular” diamonds with no discernible shape.
Dissolution experiments show that there are several factors that can impact the shape and surface features of a resorbed diamond, meaning that no two rough diamonds are exactly alike.
To find out more about how all diamonds are continuously being destroyed in the mantle, read here