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. initial public offering raised an estimated $70 million for the company, making it the second-most successful technology IPO of that year. In 2006, Blackboard completed the acquisition of its largest competitor, WebCT Inc, enlarging its share of the higher education market to between 65 and 75 percent. Over the next five years, the company invested in a series of new products and acquisitions, including Blackboard Xythos, Blackboard Connect, Blackboard Mobile, Blackboard Collaborate, and Blackboard Analytics., thus expanding beyond the learning management system market. By 2011, the firm's products were used by over half of colleges and universities in the US.