Calcium Sulfate
A salt (CaSO . H 2 O), very slightly soluble in water. In its natural form, it may exist as anhydrite (CaSO 4 ) or gypsum (CaSO 4 . H 2 O)
Source: http://palimpsest.stanford.edu/don/dt/dt0547.html
Anhydrite
Mineral calcium sulfate, CaSO4, which is gypsum without water.
Source: Leet, L. Don. 1982. Physical Geology, 6th Edition. Englewood Cliffs, NJ: Prentice-Hall
Gypsum
Hydrous calcium sulfate, CaSO4 · 2H2O. A soft, common mineral in sedimentary rocks, where it sometimes occurs in thick beds interstratified with limestones and shales. Sometimes occurs as layer under bed of rock salt since it is one of first minerals to crystallize on evaporation of seawater. Alabaster is a fine-grained massive variety of gypsum.
Source: Leet, L. Don. 1982. Physical Geology, 6th Edition. Englewood Cliffs, NJ: Prentice-Hall
Limestone
Agricultural lime is a soil additive made from pulverized limestone.  The primary active component is calcium carbonate.  Limestone’s effect on soil:

1. it increases the pH of acidic soils
2. it provides a source of calcium for plants
3. it permits improved water penetration for acidic soils