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. distance learning and for conferencing. The company launched Blackboard Mobile in 2009 after having acquired TerriblyClever. The platform provides students with access to teaching and learning content and campus information through mobile applications for iOS, Android, BlackBerry and WebOS devices. Blackboard Mobile allows students to both access course materials, check grades, and participate in discussions, and to access information about campus life and services. The company began providing its Blackboard Connect service in 2008, for use by school districts and higher education institutions to send out mass phone, text and e-mail notifications. The service can be used for routine alerts