Shape of the gem
Use the ruler to draw a triangle.
Draw a line from the lower angle to the top.
The second line starts from the same place.
It resembles a trapezoid.
If we look at a faceted diamond, we can see that it has many faces of different shapes. Draw three small triangles at the upper part. Their number coincides with the number of the lower sides.
Add the faces at the lower part. Break the upper part into smaller details.
Look at the drawing thoroughly. Correct the details. The diamond must be even.
These are the final details.
Collage of stages of the gem drawing