Nashville has a small selection of common rocks, but they tell a remarkable story.

We will consider the five most common ones, and see how much we can learn from them. (I found all of these rocks in or around Nashville, TN)

We will make observations, learn basic principles and finally make inferences from what we have seen.
 
 

Rock A - Specimen # 1	Rock A - Specimen # 2
Rock B - Specimen # 1	Rock B - Specimen # 2
Rock C - Specimen # 1	Rock C - Specimen # 2
Rock D - Specimen # 1	Rock D - Specimen # 2
Rock E - Specimen # 1	Rock E - Specimen # 2

Observations

Look carefully at each of the rocks.  What do the two specimens of each rock have in common?  How are they different?

How do the five rocks differ from one another.

When you have finished trying to answer these questions, you can look at my discussion.

       Rocks are traditionally divided into three categories, based on how they are formed

              Igneous rocks are crystalized magma which crystalizes as it rises to the surface.

              Sedimentary rocks are formed by accumulating sediment deposited in low areas.

              Metamorphic rocks are formed when heat and pressure alter existing rocks.  This usually happens where
              plates collide.

       Review how rocks are formed. Three of the five rocks in your sample are pictured on the site.  Can you find
       them?

All of the rocks commonly found in middle Tennessee are sedimentary
 

Inferences

       Judging from our evidence, do you think there have been volcanoes in Nashville?
       At the time these rocks were formed, was Nashville relatively high, or relatively low?
       Since the rocks formed, has Nashville been involved in major plate collisions?
 

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Observations

       We find limestone everywhere.  The only layer in middle Tennessee which does not contain limestone is the Chattanooga
       Shale.  In some places we find pure limestone.  In other places it is mixed with shale.
       We find shale in many layers, usually mixed with limestone.  In some places, the mixture is very shaley.  In others it is
       not.
       We find calcite and gypsum concentrated in two thin layers, one in the Nashville Group, one in the Maysville Group
       We find small nodules of chert throught all layers, and thick layers of chert in the Highland Rim.
 

General Principles

       Limestone formes from the shells of animals.  Some of these are microscopic protists, while others are larger animals.
       Limestone dissolves in acid.  Therefore, it can only form in a basic environment.  Fresh water is acidic (even without our
       intervention), while sea water is basic.  Therefore, limestone forms primarily in sea water.  Moreover, it doesn't form
       everywhere in the ocean, but primarily in warm, shallow seas.  We know this by looking at where limestone forms today.

       Shale forms when mud in the watter settles to the bottom.  We know this because chemical analysis of shale reveals that
       it is clay.

       Calcite and gypsum are evaporites.  They crystalize out of solution like sugar or salt, when solutions become
       super-saturated.  Therefore, they only form under hot dry conditions in which water is evaporating out of the ocean,
       leaving it increasingly saline.

       Chert forms in two ways.  Chert nodules form by crystalizing out of solution like calcite and gypsum.  Large layers of
       chert, so-called laminated chert, come from the shells of protists such as diatoms and radiolarians, which ahve silicon
       dioxide shells (Stones made by creatures who live in glass houses)
 

Inferences

       We know, from the presence of sedimentary rocks that middle Tennessee was in a lowland when our rocks were
       deposited.  Now we can ask, "Were we under water, and if so, was it fresh water or salt water?  Explain your answer.

       Was the water over middle Tennessee clear or muddy?  Did the amount of mud in the water remain the same over time?
       Explain your answer.

       Did the salinity (saltiness) of the water remain the same over time, or were there periods in which the water was saltier.