Really it depends on what you consider a mass of an asteroid to be. If it's large enough, the black hole is going to be releasing xrays. If it's smaller, it's

Really it depends on what you consider a mass of an asteroid to be. If it's large enough, the black hole is going to be releasing xrays. If it's smaller, it's going to be releasing gamma rays. The smaller the black hole, the faster it evaporates. The faster it evaporates, the more energy it puts out. The black hole at this scale is still going to have too small a cross section to suck up any matter and the radiation might end up blowing away any matter before it gets to the black hole in the first place. At these masses, there's no real danger in the black hole passing through the Earth itself. The only danger is how much radiation is going to be shot out as it passes through the atmosphere on either side of the planet.