Hello nautilus92,
Your description of the changa sounds weird... I don't know if you have already checked the entry of
Changa in the Wiki or the
Guide to Enhanced Leaf, but changa should not be powdery, much less silverish and solidified. Changa is supposed to look like a blend of herbs (not too ground herbs) with a slight yellow-to-light-brown resin attached to it, but even if they looked like that, you cannot tell for sure.
I get from your message that you have not prepared that changa yourself, and your concerns are one of the reasons why people prepare their own changa. Unless you perform an extensive analysis, or unless a friend shared with you his recipe, there is no way to know what's in a changa blend you haven't made yourself.
Personally, I would NOT smoke mixes that look strange and don't know what they have in them. If you are interested in trying changa, making your own is easy and will dispel any major doubts.
"The Menu is Not The Meal." - Alan Watts