1st off ALL smoke creates tar.
The tar that gets in your lungs from cigarette smoke, is a form of tobacco resin.
But there is more to Marijuana resin than that.
second element of resin is a form of butane extraction. The solvent
from the lighter is released, and together with the Cannabinoids in the
smoke, stick to the walls of a pipe.
And one more thing that makes it up,
Anything that sucked through while you were smoking. Mostly ash from
smoked material, but possibly some crumbs of unsmoked weed.
is fine to smoke, in the 60's some people actually added ash to solvent
hash to make it solid. It's not any worse for you than weed, in fact
it's possible that it can (not will) get you higher as it is a form of