What is Limestone?
How Limestone Forms
Limestone a relatively soft sedimentary rock made up primarily of calcium carbonate. This chemical compound occurs in rocks as the minerals calcite and aragonite.
Large quantities of limestone are formed from the skeletal remains of marine organisms left behind after they die. It usually forms in clear calm warm and shallow bodies of water.
Limestone is a soft mineral so scratches easily.
Colour is usually an even-white to off-white. The lustre is dull which means the surface of the stone absorbs light instead of reflecting it.
Chalk, travertine and coral are all types of limestone.
Limestone can also form very slowly over millions of years from the evaporation of water in caves. Stalactites and stalagmites which are limestone form in this way.
The limestone in our first picture comes from Arizona. The second picture is fossilferous limestone from Indiana. Both photos are courtesy of Stan Celestian. They're clickable and redirect to the original non-compressed image.