I enlarged the pic and it is a Fukien Tea, the 'teeth' can clearly be seen on the leaf ends. It looks very small when comparing it to the leaf size. I've found that the 'black' leaves and yellowing of some are a characteristic of the species. This seems to happen to all of them with older foliage as most evergreens do.

Having said that; yellowing of a lot of leaves means that the tree is overwatered or the pot is not draining well.

They will thrive with only a few hours of direct sunlight a day and when grown in a soil mix which drains well (doesn't stay wet) but stays evenly moist between waterings.

Bob