What does charcoal represent in the book Speak?

Charcoal represents Melinda's voice, which she has lost following a traumatic event at a party over the summer. Charcoal is a dark, voiceless substance, just as Melinda feels voiceless and unable to express herself after her experience. Charcoal also symbolizes Melinda's anger and the darkness she is struggling with, as well as the secrets she is keeping from those around her.