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. developer, increased Blackboard's client base to nearly 6,000 educational institutions, companies and government agencies. The company has also made acquisitions in order to expand its product base with other education-related services and software. Such acquisitions include: NTI Group in 2008, which became the basis for Blackboard Connect; providers of online and mobile collaboration tools, Wimba, Inc. and Elluminate, Inc. in 2010, to form Blackboard Collaborate; iStrategy in December 2010, which led to the creation of Blackboard Analytics; Presidium Inc. in 2011, which developed into Blackboard Student Services. Following the company's merger with Edline in 2011, Edline was later renamed Blackboard