Found a bit of info at a BBQ site:
http://www.bbq-porch.org/faq/07-10.aspMany List members have a strong preference for lump charcoal over conventional charcoal briquettes. Briquettes are produced by crushing charcoal and mixing in additives, such as nitrates (to make them burn better), and clays and starches (as binders to allow pressing into the traditional shape). Some List members say the additives tend to impart their own undesirable flavors to meats smoked for long periods of time, as all good barbecue must be prepared. A Kingsford Company spokeswoman recently stated: "Briquettes are preferred by Americans for their uniform size and stable heat." She pooh-poohs concerns about their ingredients, which include: powdered charcoal, anthracite coal for long burning, limestone to create white ash, starch as binders, and sawdust and sodium nitrate for quick lighting. "The starch is perfectly natural and the coal is high-quality coal".
Pure charcoal (lump) can usually be found with diligent searching (some supermarkets, WalMart, HQ and Home Depot, etc.). It is sold in bags similar to briquettes. Pure charcoal is carbonized wood with no additives which might impart unwanted flavors in the meat. It usually comes in the naturally irregular shapes of the real wood from which it is made. Bags of lump charcoal are usually marked with the name of the wood it was made from, i.e. hickory, mesquite, oak, etc.