You are purchasing approximately 1kg, 2.2 lbs. of high-calcium quicklime pulverized into a fine powder.  Made from ultra-pure Texas limestone, quicklime has a multitude of uses.  With a chemical formula of CaO, this powder reacts exothermically with water and produces a highly alkaline mixture.  Can be corrosive to skin and eyes, so caution must be taken, though it's not quite as bad as the safety data sheet makes it sound.  If contact with skin occurs, simply rinse with vinegar to neutralize then rinse with water.  
This quicklime averages 92% available CaO, and has <2% MgO, Fe2O3, Al2O3, and SiO2.

Quicklime (calcium oxide) has many uses in construction, agriculture, manufacturing, and environmental applications. 

Construction 
A component of cement and mortar
Used to produce lime plaster
Improves the workability and durability of construction materials

Agriculture 
Used to adjust soil pH and improve soil fertility
Used to supply calcium for plant growth
Used to combat soil acidity
Used to modify soils to minimize shrink/swell potential
Used to increase freeze/thaw resistance

Manufacturing 
Used in the manufacture of iron and steel
Used in the production of paper and pulp
Used in the production of porcelain and glass
Used in the preparation of bleaching powder, calcium carbide, and calcium cyanamide

Environmental applications 
Used in wastewater treatment and flue gas desulfurization to remove impurities
Used to modify sediments and waste streams