If you find small black spots on your cat's fur when you part it, it could be due to these reasons:
1. Skin disease: This could be caused by a skin disease or parasites. In this case, the cat may frequently scratch or bite a certain area due to itching, resulting in the fur being pulled out or broken.
For skin conditions, it is recommended to take your cat to a veterinary hospital for examination. After diagnosis, follow the veterinarian's instructions for medicated baths or topical ointments. If it is a parasite problem, consider using a flea collar for your cat and bathing them regularly.

2. Hair stains: Small black spots could also be caused by dust or other dirt on the fur. This usually doesn't have a significant impact on the cat's health, but it may affect its appearance.
It is recommended to bathe and brush your cat's fur regularly, as this will help keep their fur clean and shiny.