Blackboard ‘chalk’ are produced especially for use with blackboards in white and also in various colours. White chalk sticks are made mainly from calcium carbonate derived from mineral chalk rock or limestone, while colored or pastel chalks are made from calcium sulfate in its dihydrate form, CaSO·2HO, derived from gypsum. Chalk sticks containing calcium carbonate typically contain 40–60% of CaCO (calcite). As compared to whiteboards, blackboards still have a variety of advantages: On the other hand, chalk produces dust, the amount depending on the quality of chalk used. Some people find this uncomfortable or may be allergic to it, and according
Blackboard Inc. United States Court of Appeals for the Federal Circuit. A ruling was made by the Court of Appeals on July 27, 2009 that the 38 patent claims made by Blackboard in its suit against Desire2Learn were invalid. The dispute was resolved, when Blackboard and Desire2Learn announced on December 15, 2009 that each company was settling all ongoing litigation between them and had made a cross-licensing agreement. In April 2010, the firm abandoned patent 6,988,138, and in November that year the company's legal counsel announced the patent's "official termination" and stated that Blackboard had ended its appeals. Blackboard Inc. Blackboard Inc.