The type rock made of harden sediment is called?
Sediments harden to form sedimentary rock through the application of pressure. Heat may play a part, but it is the settling down of the sediment and the buildup of overburden that "crushes" the material together. After millenia in a "big squeeze" applied by zillions of tons of material that has been superpositioned, sedimentary rock if formed. A link can be found below to the Wikipedia post on sediment and on sedimentary rock.