Louisiana's State Gemstone: Banded Agate EarthCache
Hidden : 1/12/2010
Difficulty:
2 out of 5
Terrain:
3 out of 5

Size: Size: not chosen (not chosen)

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Geocache Description:

Welcome to the Blackwater Conservation area. This link details the history and restoration of the park after being closed as a gravel and sand quarry. Visit Website From the parking lot it is a leisurely walk along a gravel trail to a sandbar on the Comite River.

Louisiana's State Gemstone: Banded Agate




Composition:
The chemical composition of Agate is SiO2 and as such it is a form of quartz. Other forms include chalcedony, quartz crystal, or opal. Agate is a microcrystaline quartz because it shows no crystal structure to the naked eye. Color banding often occurs as a result of impurities, and these colors can range from white to brown with many rich colors.

Formation:
One of the type-localities for banded agate is north of Baton Rouge in the Amite River drainage basin. It comes from rivers eroding the Citronelle Formation which is a limestone rich layer of bedrock. The agate formed in cavities in the limestone when silica rich water permeated the rock and empty spaces allowing quartz to precipitate. This is why we see bands in the agate, as each layer deposited it contained different impurities that discolored the agate. When these nodules erode from the bedrock they are carried downstream because quartz is much harder than the limestone that enclosed it.

Gemstone?
In 1976, Louisiana adopted petrified palmwood as the official state fossil, and banded agate became the the state gemstone.

Deposition:
The freed agate is washed from the north in many of the drainages around Baton Rouge. These rivers have low gradients due to their proximity to sea level but they are still able to carry agate gravel as bedload. In a meandering system like the Comite the inside bend of the river is known as the cut bank, where sediments are eroded. The outside of the bend is known as a sand bar, where sediment is deposited. In the image below the sand bars are highlighted yellow. These are the best places to search for banded agate gravel.


The Red "X" in this satellite image shows the location of Blackwater's parking lot. From there proceed along the gravel trail to the bank of the Comite River.

In Order to log this Earthcache you must complete the following criteria
1. Take a photo of yourself near the listed coordinates with your GPS and a sample of a banded agate in the shot. (Face optional but encouraged) Upload this picture with your "Found It" log.

2. In the sand bar, dig a shallow trench in the sand with your hands or a stick, observe the layering of the strata. Do you observe variations in grain size? What do you see besides "sand"? Are there color changes? Be descriptive. (Email me a description of what this layering looks like, do not post this in your log.) Please fill in any hole you make before leaving!

I hope you have enjoyed your visit to the Comite River and Blackwater. Please remember to practice "Cache In, Trash Out" (CITO).

References:

Class Brain
SHG Resources

Additional Hints (Decrypt)

Ybbx sbe onaqrq ntngr va gur fnaqone naq gur pragre bs gur evire

Decryption Key

A|B|C|D|E|F|G|H|I|J|K|L|M
-------------------------
N|O|P|Q|R|S|T|U|V|W|X|Y|Z

(letter above equals below, and vice versa)


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