Trigons on natural diamonds

Look at these beautiful trigons on the surface of these rough diamonds! 

These are growth marks which are surface features that reflect a crystal’s development. 

Many growth marks are unique to certain crystal faces. For instance, TRIGONS - little triangular depressions- occur on octahedral faces. They point in the opposite direction from the point of the crystal’s triangular face. 

Growth marks are IMPORTANT for two reasons:

1-They help to separate diamonds from simulants (fake ones). 
2-They help cutters determine cutting directions.