leathery =? tough ??

Basils need full sun and lot of deep watering to grow green (or whatever the color) and tender.
Even partial shade is OK, (5-6 hrs sun). In full sun you have to have very good soil and water them from base, deep.
sprinklers won't do.
Rusty Color?? is it the texture of the leaves or deseased?

Read down on the first page here and you will see the same basil questions asked.

Did you just recently move them from a shady area to a sunnier area? Sun scald could cause the leaves to have a light rusty color. How about a picture.

F. DeBaggio