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. Blackboard acquired Sequoia Retail Systems in May 2016. Though previously a public company, following its 2011 buyout by Providence Equity Partners Blackboard now operates as a private company. The company's headquarters are in Washington, D.C. and it has offices in Asia, Australia, Europe and in several locations in North America. The initial product to be offered by the company was its course management software, first available in 1998. The latest version, Blackboard Learn 9.1, was released in April 2010. This is a learning management system that provides a learning system for course delivery and management for institutions; a community and