Dear
Welcome to HCM
We understand your concerns
I went through your details. Habit of eating slate pencils are due to the addiction. Addiction happens when your body craves for something. In this case, your body is deficient in some minerals, which it gets through the slate pencil. You should understand, the slate pencil is high in calcium content.
In your case, most probably, your body is craving for calcium and therefore it urges you to get calcium somehow. As you are already habituated, the easiest way is through eating slate pencils.
You may start experimenting with milk, eggs,
calcium supplements, vegetables rich in calcium etc. You may also consult a physician to check your body calcium levels. Craving can be stopped easily.
If you require more of my help in this aspect, please use this URL. http://goo.gl/aYW2pR. Make sure that you include every minute detail possible.
Hope this answers your query. Further clarifications are welcome.
Good luck. Take care.