Can't help you, Tom - I've never seen nor heard of a ceramic flint.

I did try a carbaloy flint - dull sparks & must be exceptionally sharp. A green wheel is needed for that(which isn't a problem)- the trouble comes from poor or cool sparking.

I normally use both English (Tom Fuller) flints and a chert flint napped by an American fellow over on ALR site. They are wonderful sparkers. He doesn't anneal the rock so they are very hard and most are exceptionally sharp on every side when received. Napping is must a bit more difficult than with English flints due to their hardness. Couple of my locks bounce sparks off the floor, with the 'flints'.

Some locks love them, some not so much, but all of mine do.

He calls them River Rocks.