Anyways I ended up buying Prismcolor chalk bars and as you can see the bars come in square. So I like to put in allot of fine detail and the only way to solve that problem with a square bar is to file or sharpen them. So ever so gently use a craft knife and whittle the corners off. Ever so gently if you want a sharper point you can use a regular pencil sharpener or sand paper.
Also when using a pencil sharper, be very carful because depending of the color, the bar will be softer and more brittle to breaking. But it does work faster then sitting there using a knife.
Now back to charcoal, these mix very well with charcoal and you can still use a stomp (paper rolled up into the shape of a pencil) and it blends nicely together with-out any color variations or hard edges. I hope this helps if you are working with any of these types of art supplies, you can ask me any question and I will get back to you shortly.