Limestone

I had the good fortune to grow up surrounded by limestone. In fact, the limestone rock in Cincinnati, Ohio, is world famous. The interbedded layers of limestone and shale that are seen in road cuts in and around Cincinnati make up a series of rock formations that were created in the upper Ordovician period of geologic time. This was a very long time ago, and for those keeping time it was a little over 440-million years ago.

The fossils in this limestone are of such great quality and diversity, that these formations are the world-type section of rock for this period of time. In layman's terms, this means they are the best rocks of their time. That's first place, best-in-class, or the winner.

The limestone around my childhood home had many uses. Not only was it of great interest to paleontologists, the geologists who study fossils, but it was also was/is used heavily by builders and landscapers. The rock is very dense and hard and served as a foundation material for tens of thousands of businesses and homes in the area. It also was the material used for miles of limestone retaining walls.

There are many different types of limestone. The texture of the stone in Cincinnati is very coarse. The fossils in the limestone are abundant, and it was formed in an environment similar to what you would see if you visited the Great Barrier Reef on the northeast coast of Australia.

But just 125-miles west of Cincinnati in Bedford, Indiana, you can inspect the famous Indiana limestone. This limestone is extremely fine-grained an is called an oolitic limestone. This limestone is strong, durable and easily carved. Many of the buildings in Washington, DC, use Indiana limestone on their facades. Tens of thousands of commercial and residential buildings use this magnificent and gorgeous limestone. If you look closely at it, you can see tiny fossil remains in the stone.

Crushed limestone is used by contractors and builders everyday. It makes a fantastic base for asphalt driveways and roads. This crushed stone also can serve as an excellent gravel drive or roadway by itself. The angular shapes of the stone that result as the rock is crushed allow each piece to interlock to make a very stable roadbed.

Some primary limestone uses are:

• limestone tile
• limestone flooring
• primary ingredient in Portland cement
• limestone countertops
• stone walls
• building foundations
• decorative building facades including columns, balusters, railings, etc.

Suffice it to say that limestone is used as a building material simply because of its hardness and long-term durability. Limestone is not as hard as granite, but it's hard enough that it can easily last centuries when exposed to weather.

In different parts of the Midwestern USA, you can readily see a limestone quarry or two as you drive along several interstate highways. There is a massive one southwest of downtown Chicago, several limestone quarries can be seen in northern Ohio, and there are the famous ones in Indiana. These surface mines are very distinctive as you can see the sheer faces of the limestone rock as well as active trucks, cranes and other machinery.

One other interesting characteristic of limestone is that it is the rock of choice that Mother Nature prefers to use when she constructs limestone caves. Limestone is alkaline, as it is primarily calcium carbonate. Rainwater itself can sometimes be slightly acidic and become more acidic after it falls to the ground. This acidic water seeps into the bedrock and dissolves away limestone creating massive underground caverns.

Just southeast of Cincinnati,in western Kentucky, you can visit Mammoth Cave National Park to see limestone caves that extend for miles. It's a humbling experience indeed to see how solid rock can be slowly melted away over time.

The next time you see limestone rocks, don't just brush them off. When you stop and think about it, limestone is one of the natural materials that has made America great. It's an abundant resource that's close to the surface of the earth, and we use millions of pounds of it each day in our homes, our roads and even on our roofs! Yes, limestone dust is often used to add weight to regular asphalt shingles. Can you believe that?

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