AboutDr Thomas Bell Expertise I can answer questions regarding surface earth processes and the chemical transformations that sediments and rocks undergo with burial. I can also answer questions regarding deep time, the evolution of the elements, and the last 4.5 billion years of earth history. I specialize in metallic ore forming processes, the major geologic time periods when they were produced and what they tell us about the evolution of our planet. Learn more about my professional interests at Stratamodel.com.
Experience I am a professional consulting geologist with a background in the petroleum, mining, environmental, and geotechnical industries with over 25 years of experience.
Education/Credentials Ph.D., Geology, University of California at Berkeley, 1984
M.A., Geology, University of California at Berkeley, 1980
B.S., Geology, San Jose State University, 1978
Limestone is composed of the mineral calcite which is composed of the elements calcium, carbon, and oxygen. The most common natural process responsible for limestone formation is the accumulation of minute shells of aquatic animals and crusts formed on or by aquatic plants. Limestone forms in warm climates and is actively forming in places like the Bahama Islands and the Great Barrier Reef on the east coast of Australia. If there is no source of sand and clay such as a river mouth or adjacent highland, limestone can be nearly pure calcium carbonate. Ancient limestones tend to be composed of the mineral dolomite, calcium-magnesium carbonate. Magnesium carbonate is a common 'contaminant' of limestone. It is worth noting that limestone is a major reservoir of carbon dioxide. Limestone keeps this compound locked up as a solid for millions of years and as new limestone forms, carbon dioxide is removed from the atmosphere.
Limestone is an important basic industrial commodity. Countries that lack limestone must import the most basic things at great expense.
The earliest use of limestone was as building material. In fact, that is still its primary use in one form or another. Limestone is often well bedded forming uniform thickness sheets that split into useful building blocks. If limestone is buried sufficiently deep at some time in its geologic history, the calcite grains grow larger and the limestone is transformed into marble. Great stuff to make impressive monuments, statues, or counter tops.
Sometime in the distant past, a clever human discovered that roasting limestone created a new material with very useful properties. When calcite is roasted at 800 deg carbon dioxide is released and the resulting material is quicklime (calcium oxide). When powdered then mixed with water, the lime undergoes a further transformation and sets up hard. Cement was born! Mix in a little sand and it works well as an adhesive known as mortar to hold building blocks together. Spread it on the interior walls of your hut and you have a smooth surface to decorate.
Sometime just before the common era began, the Romans took this technology a little further and invented concrete. This new building material was hard to make in large quantities and it was many centuries later before it became the common building material we use today. Those rich Romans built parts of their major port at Ostia from concrete and a remarkable building called the Pantheon in Rome.
For every 100 pounds of limestone that is calcined, 44 pounds of carbon dioxide is released to the atmosphere. The Romans weren't arguing about global warming like us but it is worth considering that global cement manufacturing is a significant source of the atmospheric CO2 generated by humans.
In the early 19th century another innovator in Britain mixed clay with limestone and roasted it. Though not invented in Portland, the material resembled stone from the Portland area of Britain thus it gained the name Portland-cement. Unlike the lime Romans used in their concrete, Portland-cement can be ground into a fine powder and stored dry until needed.
Limestone is relatively hard and brittle thus it makes pretty good road metal. Mixed with asphalt, it is used as pavement. Crushed limestone is also excellent aggregate and when mixed with portland cement makes excellent concrete.
Very pure deposits of limestone contain so few impurities that lime produced by roasting this very pure limestone is a valuable basic feedstock to the chemical industry. Lime is also used extensively in coal fired power plant stack scrubbers to remove sulfur dioxide which if released, creates acid rain.
