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. Engage. In March 2012, Blackboard acquired Moodlerooms Inc. and NetSpot of Adelaide, Australia, which then became the basis of Blackboard's Open Source Services division. From January 2014 to April 2015, Blackboard acquired nine companies, including: MyEdu, an Austin-based online education company; Perceptis, a provider of help desk and administrative services; CardSmith, a company that offered cards for student ID and on-campus payments; Requestec, a provider of technology for VoIP, video conferencing and instant messaging; and Schoolwires, a company that specialized in building school websites. In August 2015, Blackboard acquired Colombia-based Nivel7, possibly the largest Moodle services provider in Latin America.