Spherical Miracle EarthCache
-
Difficulty:
-
-
Terrain:
-
Size: 
(other)
Please note Use of geocaching.com services is subject to the terms and conditions
in our disclaimer.
This giant stone sits just north of the Joseph Smith Building on the Brigham Young University campus. There is ample free parking available in one of the visitor parking lots. See the additional waypoint provided for one nearby lot.
At the posted coordinates, you will find a large stone that is a near perfect sphere. The stone is GRANODIORITE, an igneous rock similar to granite. Granodiorite differs from granite in that it contains more plagioclase feldspar (and less orthoclase feldspar). It usually contains abundant biotite mica and hornblende, giving it a darker appearance than true granite. In addition to the large stone here, other notable examples of granodiorite are the Rosetta Stone and Plymouth Rock (a glacial erratic boulder of granodiorite).
The example before you came from a road building crew that found it in 1957 in the Diquís Delta region of Costa Rica. It has been on display at BYU since 1974-75. Carved between 200 BC and 600 AD by controlled fracturing, pecking, and grinding, this stone is remarkable for its spherical shape and great size. The original use and purpose of this stone and others like it is a great mystery, but suggested purposes include as an astronomical marker, a boundary marker, or a burial memorial.
Notice the visible composition of the stone. Pay particular attention to any crystals. Larger crystals occur when an object has cooled more slowly. In addition, look for any variation in the color of the stone. An even coloration throughout is a sign of uniform chemical weathering. By contrast, any regions that appear reddish brown in color would most likely be the result of iron oxidation, one type of chemical weathering.
To post a legitimate "found it" log on this earthcache, you must visit the site and answer these questions. Please send me a message through the Message Center feature available on geocaching.com. Do NOT post the answers in your log; I will delete any such posts. I'll also delete "found it" logs if the required logging tasks have not been completed. Non-spoiler photos are strongly encouraged--and much appreciated!
Logging Tasks (1-4 required, 5-9 optional)
1. Include the ID and name of this earthcache ("GC480JW" and "Spherical Miracle") in your email.
2. Based on the crystals that are visible on the stone, what can you say about the rate of cooling of this stone compared to a granite specimen that has crystals that measure 2 cm?
3. Is there variation in the color of the stone? Where and what (north, south, east, west)? What does that indicate about how various regions of the stone were exposed to chemical processes?
4. Based on your answer to #3, make a guess about how the stone was oriented on the ground. What is the evidence for your guess?
5. OPTIONAL. Although a photo at the site is not required, please post a photo of yourself that DOES NOT SHOW the stone or the plaques.
6. OPTIONAL. For what do you think this stone was used? As mentioned, suggested purposes include as an astronomical marker, a boundary marker, or a burial memorial. Does one of those sound right to you? Feel free to offer your own whimsical or humorous (but FAMILY FRIENDLY) answer.
How Much Does It Weigh? (Tasks 7-9 are all OPTIONAL exercises that bring in some mathematics. Not all stones can have their volume and weight closely estimated by formula!)
7. What is your estimate of the DIAMETER of this stone? (Include a unit, such as feet, inches, meters, or centimeters.)
8. In terms of its diameter, d, the volume of any sphere is (╥/6)*(d^3). ╥ (pi) is the mathematical constant nearly equal to 3.14. Using your estimate from #7, what is the VOLUME of this stone? (Again, include a unit, such as cubic feet, ft^3.)
9. The density of granodiorite is about 2600 kg/m^3 or about 160 lb/ft^3. Using your estimate from #8, what is the WEIGHT of this stone?
Thanks for visiting! For more information about earthcaches, please visit www.earthcache.org.
Selected Sources:
http://en.wikipedia.org/wiki/Granodiorite
Lewis, T. J. & Bentkowski, W. H. 1988. Potassium, Uranium and Thorium Concentrations of Crustal Rocks: a Data File. Geological Survey of Canada, Open File. http://books.google.com/books?id=r2wYo1l4rScC
Additional Hints
(No hints available.)