A small fragment of sediment acts as a 'seed', perhaps something like a piece of sea shell. As strong currents wash these 'seeds' around on the floor of the sea, they accumulate layers of chemically precipitated calcite from the water. After ages of time, they form into small grains of sand.
More ages pass, and they form together into sand dunes under the surface of the water. Millions of them pushed into one place, the calcite keeps forming around them until the weight of the layers above compresses them and the chemicals bind them into clumps.
More thousands of years pass, and finally they have been pushed into their smallest possible form, filled with calcite and joined by millions of other small pieces they become a formation of Oolitic limestone.
This sample is from Gloucestershire, England.
Here in the States, this wonderful stone contributed the materials for such U.S. landmarks as the Empire State Building in New York and the Pentagon in Arlington, Virginia. Many of the buildings on the Indiana University campus in Bloomington are built with native oolitic limestone material. (Credit: Wikipedia)
These photos are from a thin section slide of Oolitic limestone from England, cut and polished to a thickness of 30 microns. So thin that light can pass through, it forms fascinating patterns under the microscope.
These slides are from a company called the Geology Superstore. Located in England, these folks are wonderful to do business with, and have some incredible slides if you are interested. I don't usually do commercials , but I am so happy with the material they sent me I had to mention them.