Could be all sorts, did he tell you any sort of dosage information? It could be compressed kief of some kind or it could be a synthetic cannabinoid - big difference, since kief you can pack a pipe load like you would with weed, only it'll be a lot stronger, where with synthetic cannabinoids with most of the ones currently legal/available the dosage starts at less than half a milligram, meaning 1/2000th of a gram.. Ask the person the dosage and the name of the exact cannabinoid, and start with half a milligram to be safe.
If it's a synthetic cannabinoid don't even try smoking it without a scale, synthetic cannabinoids are NOT pleasant to overdose on.. imagine smoking 10 joints with no tolerance in a matter of seconds all at once, straight to paranoia-land thinking you're about to have a heart attack.
We can't identify your drugs for you. Brown powder could mean thousands of different drugs or inactive substances.