Date: Fall 2011
What happens when rocks dissolve? What evidence is there for rocks dissolving? What is left behind, if anything?
There are a lot of reasons why rocks dissolve: some include research whereas others are natural. Have you ever seen the black squiggly (somewhat jagged looking) lines in marbles? This interdigitated fabric results from the
dissolution of carbonate minerals (usually the lighter colored minerals) against the insoluble darker minerals. The carbonate goes into solution, finds its way through cracks in the rocks and may show up as carbonate veins elsewhere. Read about the formation of stylolites.
Acid rain also dissolves rocks. Look at the façade of numerous buildings and marble statues, and marble headstones that have been outside for years. The acid is neutralized by the carbonate.
These are only two ways in which rocks dissolve.
Rocks do dissolve in water.
What happens when rocks dissolve?
It depends on where the rocks are.
If you can, visit a limestone cave in your locality.
There the rocks are underground and when they dissolve in water they leave a cave.
Check out this URL about Carlsbad Caverns:
Google "Carlsbad Caverns" and you will find photos if there aren't any caves in your locality.
If the rocks are on the surface, they just dissolve into the water and form mineral water.
Sometimes the mineral water drains into underground aquifers like the Ogallala aquifer in the Midwest.
Please see this URL:
People whose drinking water is mineralized usually have stronger teeth and bones due to the additional minerals in their water. Of course this depends on what minerals are in the water and how much.
What evidence is there for rocks dissolving?
The caves I mentioned above and if you check around the tips of the faucets in your home you may find mineral deposits from minerals in your home drinking water.
What is left behind?
Water erodes rocks to sand and earth. Another contribution to rock break down is the cycle of freezing and thawing.
You can see the result of what is left behind at the base of cliffs. I'll attach a picture that shows the build-up of rocks that are broken down to sand and earth at the base of a cliff.
By dissolving, I assume you are talking about what geologists call chemical weathering which breaks up rocks where they stand. Water of some sort is usually involved.
Rocks rarely "dissolve" all at once. The most susceptible minerals usually go first depending upon their position in Bowen's Reaction series. The first to crystallize in the series are the first to break down.
Simply put, rocks usually do not dissolve like a lump of sugar in a hot drink. Some minerals are converted to another mineral which cannot hold the rock together and, it falls apart. In some cases, what is left of the rock is washed away by rain or streams.
In granite, the feldspars are changed to clays and the rock falls apart leaving quartz (sand) and sometimes mica. If the granite has hornblende, these often dissolve first.
The evidence for a "dissolved" rock is often a pile of weathered minerals that look like someone dumped them there. Other times it is a bunch of sand. It depends upon the rock's composition what it leaves behind.
Over time geologists have found rocks in the process of breaking down and have a good idea as to what happens.
Looking up "chemical weathering" will probably give you more than enough information.
Hope this helps.
R. W. "Mr. A." Avakian
Oklahoma State Univ. Inst. of Technology
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Update: June 2012