I'm curious as to where you found this alleged diamond with trigons. Is the crystal clear (it can have color)? Are there distinct, measurable "steps" between the levels of trigons? Can you separate one of the trigons from the remainder of the crystal with something like a knife blade? Other than the surface irregularities, what is the general shape of the crystal? Have you trotted over to a local jeweler to have it tested?
If the crystal is, in general, hexagonal and has a step-wise progression of that could be confused with trigons, you could have a sample of bismuth. Remember, trigons, when found on diamonds, don't stack in a regular pattern, rather, they occur at points of natural cleavage lines.