Limestone composed almost entirely of crinoid (marine animal fossil) stem plates, from near Columbia.
Pure limestone is composed of 100% calcium carbonate (calcite mineral), whereas pure dolomite contains 54.35% calcium carbonate and 45.65% magnesium carbonate (dolomite mineral). Magnesium carbonate has slightly higher acid-neutralizing properties than calcium carbonate, weight for weight, and because analyses of limestone to be used for soil sweetening and agricultural fertilizer purposes are commonly reported in calcium carbonate equivalents, a dolomite or dolomitic limestone may be reported over 100% calcium carbonate equivalent. Unless one understands the full meaning of the report he may be bewildered by a statement of the value over 100%.
The calcium and magnesium which form limestone (or dolomitic limestone) in the ocean are carried there in solution by the streams which drain the land. Rain water percolating through the ground and rocks becomes slightly acidified with carbon dioxide (like the carbonated water in beverages) and dissolves the calcium and magnesium from primary igneous rocks like gabbro and basalt which are weathering, or from preexisting limestones which primitively were derived from igneous rocks. This calcium and magnesium in solution are responsible for the hardness of the water. In fact, the hard water in Missouri springs, wells, and streams is hard because it contains either or both calcium (“lime”) and magnesium in solution.
This soluble calcium and magnesium flows on in the stream to the ocean because of its combination with the dissolved carbon dioxide. In the shallow parts of the ocean, as on the continental shelves where the water is less than 600 feet deep, the limestone is deposited in layers just like the white lime layer deposits on the bottom of the teakettle in which hard water has been boiled. Chemical processes, temperature changes, evaporation of the ocean water, and organisms are responsible for most of the limestone deposition. Extensive limestone deposition is taking place today off the coast of Florida and around the tropical islands of the southern Pacific.
The uses of limestone are numerous. It is an excellent building stone in either the rough, sawn, or dressed state. It is used for rubble stone, rip-rap, railroad ballast, crushed gravel, and aggregate in concrete. It is one of the raw materials of Portland cement. Quicklime and hydrated lime are prepared from limestone which has been heated to drive off the chemically combined carbon dioxide.
Limestone is added as a fluxing material in metallurgical processes. It is the lowest priced source of alkali in chemical industry. Pulverized limestone may be used as a filler in paints, putty, paper, or rubber; and rock wool is made by melting and blowing a limestone having a suitable chemical composition. Two formations develop a “spongy” appearance (“sponge rock” or “sponge limestone”) upon weathering and are utilized abundantly in the eastern part of the state for rock gardens and for ornamental and decorative stone.
Many tons of limestone are used each year in Missouri as a soil fertilizer because it neutralizes acidity, coagulates the clay, furnishes calcium to the plants by way of the colloidal clay, and frees other chemical elements so that they become available to the plants. No doubt rocks other than limestone will be crushed and added to the soil in the future, but today our attention is focussed chiefly on limestone and dolomite.
The value of a limestone quarry for agricultural purposes depends upon availability, amount of overburden, purity of the stone, ease of crushing, and size of deposit. For instance, a stone of 90% purity, which is close at hand, will probably be more valuable than one of 98% purity which must be hauled fifteen miles. Bare hillsides or creek banks where a crusher can be set up to handle the stone without extra lifting are preferable for quarry sites. Usually the overburden is less in such an exposed face. Impurities in limestone deposits may be large chert (flint) nodules which can be hand-sorted out, sand grains, clay which settled into and onto the stone during its accumulation, and pyrite (fool’s gold) or other minerals of lesser importance. Clay impurities simply act as useless extra weight which must be handled. Sand grains, however, are hard, and will abrade and wear out crushing equipment. Chert and fine-grained silica likewise are harder than steel and will wear a crusher excessively. Pure limestone (calcite or dolomite mineral) has a hardness less than that of steel and will only polish or wear the metal slightly.
Typical, intermittently-operated, farm limestone quarry near North Kansas City.