Reminder concerning "Earthcaches": there is neither a container to look for nor a logbook to sign. One need only go to the location, answer to the differents questions and send us the answers.
The Earthcache
Evanston Plaza is a small square with imposing blocks of rock representative of the three major geological families existing on Earth: sedimentary, metamorphic and magmatic.
► Sedimentary rocks
A sedimentary rock is formed by diagenesis from sediments deposited and then cemented.
There are two types of rocks according to the biogenic or detrital origin of the sediments.
~ Biogenic sedimentary rocks, limestones
These rocks come from the remains of living organisms accumulated in warm, shallow waters.
These debris, hard elements made up of calcium carbonate (shell, skeleton, etc.) consolidate into limestone, a white rock with numerous traces of fossils.
~ Detrital sedimentary rocks
They are formed of solid terrigenous debris (little or not biological) cemented together.
These rocks therefore have few or no fossils, often have stratification and are characterized according to a grain size classification (grain size).
► Metamorphic rocks
These are secondary rocks derived from a protolith that has undergone transformations under the effect of temperature and/or pressure changes.
These are crystalline rocks, hard, very varied. Here are some examples :
- Micaschite: transformation of a very fine-grained detrital sedimentary rock (clay), giving a non-grainy rock organized in very fine sheets ("thousand sheets").
- Marble: transformation of a limestone sedimentary rock with crystallization into finely grained white calcite. White color if pure, colored if mineral oxides present.
- Migmatite: under high pressures and temperatures, partial melting then recrystallization giving a mixture of light molten structures in a vein and dark areas that have never melted. Rock with a chaotic structure with many veins or very folded beds.
► Magmatic rocks
Resulting from the crystallization of a molten magma, they are entirely crystalline and hard rocks which are classified into two types.
~ Volcanic rocks or extrusive rocks.
They come from a magma which is introduced into the earth's crust up to the surface and gives rise to lava flows.
Because of this rise, cooling and crystallization are rapid, giving very small crystals that cannot be seen with the naked eye (eg basalt, dark, homogeneous and not grainy).
~ Plutonic rocks, or intrusive rocks.
They come from a magma which got stuck in the crust and slowly crystallized there.
The slow lowering of the temperature gives time to form crystals visible to the naked eye. The best known example is granite composed of 3 crystals (Quartz: gray and translucent mineral without facet; Feldspar: opaque whitish; Mica: opaque and shiny black mineral).
► Bibliographical sources
The Questions to validate "A World of Rocks at Evanston Plaza"
A careful reading of the description of the cache, as well as observation of terrain features and some deduction is usually sufficient to answer questions of this EarthCache.
You are now in Evanston Plaza. Use photo WP1 to determine the different rocks to study and identify.
- Question 0 : Take a photo of yourself or of an element identifying you on site, without showing the observation areas.
This photo will have to be sent to us with the answers or to be added to your log.
- Question 1 : Describe the rock behind the red zone A. Deduce its family, its sub-family (type) if there is one and finally its nature by explaining your reasoning.
- Question 2 : Describe the two rocks behind the green zone B (these are the same type of rock). Deduce its family, its sub-family/type if there is one and finally its nature by explaining your reasoning..
- Question 3 : Describe the rock behind the blue zone C. Deduce its family, its sub-family/type if there is one and finally its nature by explaining your reasoning..
- Question 4 : Describe the rock behind the yellow zone D. Deduce its family, its sub-family/type if there is one and finally its nature by explaining your reasoning.
You can log this cache without waiting for our confirmation,
but you must send us the answers at the same time, by e-mail via our profile (
fafahakkai) or by the system of Message Center of geocaching.com.
If there is a problem with your answers we will notify you.
The logs recorded without answers and photo will be deleted.