Chalk produce, and thus widely used in the developing world, calcium-based chalk can be made where the crumbling particles are larger and thus produce less dust, and is marketed as "dustless chalk". Colored chalks, pastel chalks, and sidewalk chalk (shaped into larger sticks and often colored), used to draw on sidewalks, streets, and driveways, are primarily made of gypsum. Chalk is a source of quicklime by thermal decomposition, or slaked lime following quenching of quicklime with water. In southeast England, deneholes are a notable example of ancient chalk pits. Such bell pits may also mark the sites of ancient flint mines,
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.