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. initial public offering raised an estimated $70 million for the company, making it the second-most successful technology IPO of that year. In 2006, Blackboard completed the acquisition of its largest competitor, WebCT Inc, enlarging its share of the higher education market to between 65 and 75 percent. Over the next five years, the company invested in a series of new products and acquisitions, including Blackboard Xythos, Blackboard Connect, Blackboard Mobile, Blackboard Collaborate, and Blackboard Analytics., thus expanding beyond the learning management system market. By 2011, the firm's products were used by over half of colleges and universities in the US.