Particles like that would be ordinary matter. In the quantities necessary to produce the effects attributed to dark matter, we would be able to detect them easi

Particles like that would be ordinary matter. In the quantities necessary to produce the effects attributed to dark matter, we would be able to detect them easily. Even if they remained "dark" - not emitting any light of their own - they would block or otherwise interfere with the light coming from everything behind them. The reason PBHs can be a dark matter candidate is because they can compress enormous amounts of matter into a very small space, and are difficult to detect when they're not interacting with ordinary matter.