All major calcium compound interconversions:

$CaCO_{3}$ (Limestone)
   |
   | heat 1073 K, -$CO_{2}$
   ↓
CaO (Quicklime)
   |                           \
   | + $H_{2}O$ (exothermic)        | + $CO_{2}$ + $H_{2}O$ (from air slowly)
   ↓                            ↓
Ca(OH)_{2} (Slaked lime)         $CaCO_{3}$ (reformed — whitewashing)
   |
   | + $Cl_{2}$
   ↓
CaO$Cl_{2}$ (Bleaching powder)

$CaSO_{4}$·2$H_{2}O$ (Gypsum)
   |
   | heat at 373 K (partial dehydration)
   ↓
$CaSO_{4}$·½$H_{2}O$ (Plaster of Paris)
   |
   | + 3/2 $H_{2}O$ (setting)
   ↓
$CaSO_{4}$·2$H_{2}O$ (Gypsum — reformed, exothermic, slight expansion)

   Above 393 K from Gypsum:
   $CaSO_{4}$ (anhydrous, dead-burnt) — does NOT set

$CaCO_{3}$ + 2HCl → Ca$Cl_{2}$ + $CO_{2}$ + $H_{2}O$
Ca(OH)_{2} + $CO_{2}$ → $CaCO_{3}$ + $H_{2}O$ (lime water test)
$CaCO_{3}$ + $CO_{2}$ + $H_{2}O$ → Ca($HCO_{3}$)_{2} (temporary hard water)