From the passage identify the usage of Limestone. Display the results in a numbered list format.
Limestone��(calcium carbonate��CaCO3) is a type of��carbonate��sedimentary rock��which is the main source of the material��lime. It is composed mostly of the��minerals��calcite��and��aragonite, which are different��crystal forms��of��CaCO3. Limestone forms when these minerals��precipitate��out of water containing dissolved calcium. This can take place through both biological and nonbiological processes, though biological processes, such as the accumulation of corals and shells in the sea, have likely been more important for the last 540 million years.��Limestone often contains��fossils��which provide scientists with information on ancient environments and on the��evolution��of life.About 20% to 25% of sedimentary rock is carbonate rock, and most of this is limestone.��The remaining carbonate rock is mostly��dolomite, a closely related rock, which contains a high percentage of the mineral��dolomite,��CaMg(CO3)2.��Magnesian limestone��is an obsolete and poorly-defined term used variously for dolomite, for limestone containing significant dolomite (dolomitic limestone), or for any other limestone containing a significant percentage of��magnesium.��Most limestone was formed in shallow marine environments, such as��continental shelves��or��platforms, though smaller amounts were formed in many other environments. Much dolomite is secondary dolomite, formed by chemical alteration of limestone.��Limestone is exposed over large regions of the Earth's surface, and because limestone is slightly��soluble��in rainwater, these exposures often are eroded to become��karst��landscapes. Most��cave��systems are found in limestone bedrock.Limestone has numerous uses: as a chemical��feedstock��for the production of��lime��used for��cement��(an essential component of��concrete), as aggregate for the base of roads, as white pigment or filler in products such as��toothpaste��or��paints, as a��soil conditioner, and as a popular decorative addition to��rock gardens. Limestone formations contain about 30% of the world's��petroleum reservoirs.
1. as a chemical feedstock for the production of lime used for cement (an essential component of concrete)
 2. as aggregate for the base of roads
 3. as white pigment or filler in products such as toothpaste or paints
 4. as a soil conditioner
 5. as a popular decorative addition to rock gardens