Using the lapidary skill, you are able to shape gems into many different forms.
If you have a blue sapphire and you use the command shape in this way;
Shape sapphire 'Crescent moon'
You will get: A blue sapphire shaped as a/an crescent moon
"Shaped as a/an" will be included automatically with the desired shape, if you aren't sucessful in your shaping of the gem either will not happen anything to the gem or it would be destroyed (Hopefully if it is destroyed you would get some gem powder, although not always)