Roadside Geology 01 - West Texas Caliche EarthCache
Hidden : 1/14/2011
Difficulty:
2.5 out of 5
Terrain:
2 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

Easy parking on the dead end spur, level terrain but beware the mesquite and typical West Texas flora and fauna. be sure to bring some lemon or lime juice, or vinegar!

Welcome to my first Roadside Geology Earthcache!


Caliche





For this Earthcache you will need to bring a small bottle of weak acid with you. This can be lemon or lime juice, vinegar, or a diluted HCL solution if you have access to some.


Caliche is a sedimentary rock deposit of calcium carbonate (limestone) although it may contain impurities of many other minerals. In West Texas as well as most of the arid to semi-arid southwest United States it is found abundantly in the near-surface. It is relatively soft and fissile (crumbles), and can range in color from white, to cream, to pink and red. Caliche is the Spanish word for lime (calcium carbonate, not the fruit).


The bedrock of West Texas is, in large part, composed of limestone and dolomite. Caliche is formed when ground water rich in dissolved calcium carbonate from these source rocks leaches up into the soil, then evaporates or retreats, leaving the calcium carbonate behind. Over time these soils are weathered by wind and rain, some soil is removed leaving only the hard cement-like caliche behind. This is why it is sometimes referred to as hard pan, because of the hard in penetrable surface of exposed caliche in the soil.

Caliche is used in construction as an ingredient in cement, and as a pH balancer in soil as it is a fairly strong Base (pH >7). It is also used as fill material and roads, but only in arid regions as it does not stand up to water well. In the sugar refining industry, pure caliche can be used in lieu of other forms of calcium carbonate when they are not readily available locally.


As any West Texas gardener will tell you, caliche causes many problems in gardens and flower beds. It stops water from properly draining from a bed and makes the soil Basic. It can also block the transport of oxygen and minerals to the roots of plants, especially iron. And it can cause excess salt build-up in the soil as it weathers.



To Log This Earthcache email me with the following:
1: Describe what occurs when you place a drop or two of your acid on a piece of caliche. (reaction, sound, smell, sight). Why do you think this happened?
2: Look around you at the caliche strewn about, do you believe this is in-situ (in place)? Why or why not?
3: This rock is sedimentary, do you believe it is a result of Primary (by wind, water, erosion) deposition, or Secondary (chemical) deposition? Why?
4: Math Time: Find an exposed piece of caliche that has good visible banding, measure the thickness in centimeters. In the Permian Basin the average rate of deposition is 2.1 cm/yr! How many years do you calculate it took to deposit this caliche?
5: Optional Post a photo with your log of your experience, experiment, or just the scenery. Have fun!



Information Sources and Further Reading:
Wikipedia entry on Caliche
An Abstract on Caliche Fromation
Google Answers article on Caliche

Additional Hints (No hints available.)



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