I advise to not use substrate at all.
With other reptiles you may use substrate, but usually with a chameleon you want a tall, ventilated cage, and usually they like being at the top..
So for one, if the chameleon is on the floor you've already got an issue (unless it is female and is looking for digging spots) because they love being up high.
Second, the chameleon could choke on the dirt.
Just don't use substrate.
You may use substrate for insects like superworms and mealworms