Things you will need to log this Earthcache:
- GPS
- Camera (optional)
To log your find, please E-mail me via my profile, the answers to the following questions:
- List all of the different colors that you see in the quartzite in the order of most to least.
- Locate the ripple marks and tell me what the angle is from horizontal. No need to climb to measure, just your best guess.
- Two type of metamorphic rock are defined below. The me which type this Quartzite is. Either Foliated/Banded or Non-Foliated/Granular.
- Not required but always appreciated, post to your on-line log a photo of your GPS. Your face can be included if you so wish.
Definition of Terms
Metamorphism
Occurs when any previously existing rock has been modified by heat, pressure or chemical processes usually while buried deep below Earth's surface. The deeper the rock is buried the hotter it gets, and the higher the pressure becomes. Eventually, rock must adjust to the new conditions, whether it is baked, or squeezed, or both, and in the process becomes a metamorphic rock. At the extreme end of metamorphism melting takes place. The melting temperature for a rock ranges from a low of 1300-1500 degrees F to as high at 1800 degrees F. The resulting rock types are know as metamorphic rocks.
There are two basic types of metamorphic rocks: 1) foliated metamorphic rocks such as slate, schist and gneiss which have a layered or banded appearance that is produced by exposure to heat and directed pressure; and, 2) non-foliated metamorphic rocks such as marble and quartzite which do not have a layered or banded appearance.
Foliated/Banded
Are formed within the Earth's interior under extremely high pressures that are unequal, occurring when the pressure is greater in one direction (as shown by the longer arrows) than in the other direction. This causes the minerals in the original rock to re-orient themselves with the long and flat minerals aligning perpendicular to the greatest pressure direction. This reduces the overall pressure on the rock and gives it a stripped look. The layering produces three distinctly different looking rocks, those with slaty cleavage (slate), schistosity (schist), and mineral banding (gniess).
Non-Foliated/Granular
Are formed around igneous intrusions where the temperatures are high but the pressures are relatively low and equal in all directions (confining pressure). The original minerals within the rock re-crystallize into larger sizes and the atoms become more tightly packed together, increasing the density of the rock.
Ripple Marks
A series of small marine, lake, or river sedimentary structures, consisting of repeating wavelike forms with symmetrical slopes, sharp peaks, and rounded troughs. Ripple marks are formed in sandy bottoms by oscillation of waves.
The Geology
Two billion years ago the North American continent did not exist as we know of it today. Through collisions with other landmasses the continent grew in size. As a result of these collisions mountains grew and basins were formed. As the mountains eroded, the basins were filled with various sediments which formed different types of rock, such as Limestone, Shale and Sandstone.
Through the millions of years the sediments grew in thickness. Older deposits were buried deeper and deeper. The continued collisions of land masses helped to increase the pressure and temperatures of the sediments. The increased pressure and temperatures caused the deepest rock layer to change into a different type of rock. This process is know as metamorphism. The collisions also caused the rock layers to be folded or tilted.
As a result of the increased temperatures and pressure Limestone becomes Dolomite, Shale becomes Slate and Sandstone becomes Quartzite. It is the later that is the focus of this Earthcache. As you stand at the posted waypoint and look south, you will see a road cut into a formation known as the Ajibik Quartzite. This rock is a member of Menominee Group, which is part of the Marquette Range Supergroup. It's age is from 1.8 to 2.1 billion years or from the Middle Precambrian age. This rock was originally sandstone that was deposited in shallow water. Proof of this can be seen in a small area of ripple marks two thirds of the way up the rock face. The Ajibik Quartzite, averages 150 feet thick and consists of white to purplish-gray, ripple-marked, and cross-bedded quartzite.
Quartzite is a non-foliated metamorphic rock that is produced by the metamorphism of sandstone. It is composed primarily of quartz. The traditional way to distinguish quartzite from sandstone is that quartzite fractures across or through the grains whereas sandstone splits between them.
References used:
- http://csmres.jmu.edu/geollab/fichter/MetaRx/index.html
- http://www.minsocam.org/MSA/K12/rkcycle/metamorphic.html
- http://geology.com/rocks/metamorphic-rocks.shtml">
- http://www.michigan.gov/documents/deq/GIMDL-RI21_216264_7.pdf