This is an Earthcache – as such, there is no physical cache. Instead after examining the granite at the posted coordinates, you will answer 4 questions, and then message me the answers to claim a find. This Rest Area is located in Arkansas at exit 279A, and only accessible from Westbound Interstate 40.
This earthcache features a block of granite engraved with Arkansas The Natural State. The purpose of this earthcache is to introduce only the basics about granite while travelers are taking a break from interstate driving. The main lessons that will be covered are about the formation of granite, crystal sizes, and what minerals give granite it's different colors.
Granite is an intrusive igneous rock that begins as a molten liquid state that solidifies as it cools. The texture is now determined by the rate in which it cools. The large mineral crystals in granite are evidence that it cooled slowly from molten rock. That slow cooling occurred beneath the earth's surface and required a long period of time. Granite which cools closer to the earth's surface as when it is exposed to air or water, cools more rapidly and the result is a granite with crystals that are smaller.
Granite comes in a wide variety of colors--greens, whites, browns, yellows, blues, blacks, reds, grays, and more. The relative proportion of the different colored minerals in a granite is largely due to the original source of molten rock that cooled to form the granite.
So if the molten rock was abundant in potassium feldspar, the granite is more likely to take on a pink color, and if the molten rock was abundant in quartz and minerals that make up amphibole you will likely get a black and white speckled granite.
I managed to locate blueprints for three of the 13 Arkansas Welcome Centers. Each of these three prints specified that these Arkansas The Natural State signs to be of polished and engraved granite. The Helena Welcome Center called for Texas Pearl from the Cold Springs Granite Company, while the Red River and Harrison Welcome Center's specifically called for China Gray Granite from the Dakota Granite Company.
As you can see in the two pictures above, both Texas Pearl and China Gray each have their own distinct mineral and color make up. The China Gray has smaller black, white, and gray crystals, while Texas Pearl has a nice light pink tone, especially noticeable on the polished areas of the stone.
LOGGING REQUIREMENTS:
To log this Earthcache: Read the geology lesson above. Answer all four questions posted below. Answers can be sent via e-mail or messenger contacts on my Geocaching profile within a reasonable time. Group answers are fine, but do not post the answers to the questions in your logs.
QUESTION 1. Is this igneous stone EXTRUSIVE or INTRUSIVE? Why?
QUESTION 2. Tell me the average size of the biotite crystals in the granite rock. (Example: The biotite crystals are the size of a dime, or the size of a grain of rice, or the tip of a pencil... be creative in what you use.)
QUESTION 3. Using the colored mineral chart above, look at the rock and tell me the main 3 minerals that you see that make up this granite?
QUESTION 4. Do you think that this granite is Texas Pearl, China Gray, or a different Granite?
OPTIONAL PHOTO: Posting a photo that readily indicates that you (and anyone else logging the find) are at the location.
Awesnap has earned GSA's highest level:
REFERENCES:
1. China Gray from Dakota Granite, J.Rogers, Granite Sign Detail, Arkansas Welcome Center Reconst. (Red River), Job 030449, pg.24, ardot.cgov
2. Texas Pearl from Cold Springs Granite, J.Rogers, Granite Sign Detail, Arkansas Welcome Center (Helena - West Helena), Job 110536, pg.19, ardot.cgov
3. China Gray from Dakota Granite, J.Rogers, Granite Sign Detail, Arkansas Welcome Center Reconst. (Harrison), Job 090427, pg.26, ardot.cgov
4. What is Granite? What is Granite Used For?, H.M.King, website, geology.com
5. What Makes Up Rocks?, Lesson Rock Solid, Teach Engineering, website, teachengineering.org