Some of what I have read here leads me to believe that a TIA is a stroke that totally reverses itself and all symptoms go away within 24 hrs. Other postings indicate that if symptoms continue or periodically return, then that is an indication that it was more than just a TIA or that there are continuing problems.
Chalk /ËtÊÉËk/ is a soft, white, porous sedimentary carbonate rock, a form of limestone composed of the mineral calcite. Calcite is calcium carbonate or CaCO 3.It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite shells (coccoliths) shed from micro-organisms called coccolithophores.he most common forms are CaCO 3 (calcium carbonate) and CaO (calcium oxide). Small doses of chalk can also be used as an antacid. Additionally, the small particles of chalk make it a substance ideal for cleaning and polishing.
(April 2008). A quadruple blackboard at the Helsinki University of Technology. A blackboard (UK English) or chalkboard (US English; also blackboard) is a reusable writing surface on which text or drawings are made with sticks of calcium sulfate or calcium carbonate, known, when used for this purpose, as chalk.ticks of processed chalk are produced especially for use with blackboards in white and also in various colours. These are often made not from chalk rock but from calcium sulfate in its dihydrate form, CaSO 4 Â·2H 2 O (gypsum). Chalk sticks containing calcium carbonate typically contain 40-60% of CaCO 3 (calcite).