Respirator or mask for brick (crystalline silica) and mold?
Respirators are more typically used for preventing inhalation of gaseous contaminants which aren't filtered by simple fabric masks. They force air through media which entrap those gases. While they will also catch particulates, they're usually overkill for situations with just that concern. In your case, both silica dust and mold spores are particulates, with no real gaseous hazards involved.

Masks are simple dust filters, and the N95 spec indicates the size of the particulate that will be protected against. Search 'N95 mask' and you'll see a plethora of inexpensive options to meet your needs. These offer the added benefit of not making you look like a CDC operative while doing simple home improvement work.

I'd look for one with dual straps (for better mask-to-face seal integrity), and the exhaust vents some offer prevent forceful exhalation from creating gaps at the face-to-mask seal by more effectively venting pressure.