Crime to Court offers a video special here . Marijuana is likely the most common and officers know what that looks like. Powered cocaine is a little difficult to identify conclusively. It's a simple white powder. Field testing is needed for probable cause to make an arrest.
Rocks can be any size and sell for various prices.
Another street drug is heroin . Heroin may be sold in different color bags. These bags may have a variety of names such as Little Executioner, which allows the purchaser to ask for the product by name. It is sometimes hard to tell. With marijuana, generally, they act like they are not all there.