Calcium sulfate an unusual property: when mixed with water at normal (ambient) temperatures, it quickly reverts chemically to the preferred dihydrate form, while physically "setting" to form a rigid and relatively strong gypsum crystal lattice: This reaction is exothermic and is responsible for the ease with which gypsum can be cast into various shapes including sheets (for drywall), sticks (for blackboard chalk), and molds (to immobilize broken bones, or for metal casting). Mixed with polymers, it has been used as a bone repair cement. Small amounts of calcined gypsum are added to earth to create strong structures directly from cast earth, an
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