Science Buddies: "Ask an Expert"

This isn’t for a school project, but just for curiosity. I am an odd person and, when it rains, I like to put out a bucket or tub and see how much water it collects. Every single time I do this there are tiny rock/mineral particles inside the container. I read that rain needs DUST particles to form, but keep in mind, what I am seeing are visible, black, rock/sand-like particles. (I searched google about this but it only pulled up topics about how rain erodes rocks and whatnot. Thanks, google!) So I googled “Ask a professional” and hey, this website exists! Thanks to anyone who can give me an answer

Hello Nathan,
The Science Buddies Ask the Expert forum is only for students in grades K-12 who are doing science projects. There are other websites on the web where your question would be more appropriate. Thank you.