You need to get all the growstones out ASAP...I believe they are white..right? For some reason chameleons are attracted to white things. The lava rock needs to go too...ASAP.If your chameleon continues to eat the stones and lava rock sooner or later he will end up!impacted and dead.
Don't use moss...it can cause impaction too.
Some soils and some sands seem to pass through them without causing impaction but the problem is figuring out which ones work without creating an impaction...which is why we tell people not to use a substrate as a rule.
I also recommend adding greens (dandelions, kale, endive, escarole, etc), veggies (carrots, sweet potato, sweet red pepper, zucchini, squash, etc) and a bit of fruit (berries, melon, apples, pears, etc) to the diet of crickets, roaches, superworms, etc.
It's thought that chameleons eat soil and rocks, etc because they are missing nutrients in their diet...as was already said.
Hope all goes well!