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
The most prestigious buildings on Seattle's First Avenue use materials considered noble and aesthetic, marble stones.
But is not marble who wants!
► Marble or not Marble, that is the question
The term "marble" is a traditional name derived from the Greek marmaros, which means "resplendent stone" and indicates any "polishable" stone.
In this sense, the name has no precise geological definition and only refers to the ability of a rock to be polished and reflect light.
Let us detail the main marble rocks, including of course real marble.
► Granite Marble
Granite is an entirely crystalline rock with a grainy texture (millimetric to pluri-centimetric crystals).
It is also characterized by its hardness (not scratchable with metal) and a complete absence of orientation of the crystals between them (no foliation, fold or deformation).
It is mainly made up of 3 minerals:
- Quartz: translucent sometimes transparent, gray mineral without facet.
- Feldspar: opaque to translucent mineral, whitish or pink (orthose).
- Mica: opaque and shiny black mineral (biotite) or pearly white (muscovite).
► Migmatitic Marble
Migmatites are metamorphic rocks often derived from an acid protolith (granite).
They are therefore grainy, very hard and have the same chemical composition as granite.
The main difference with a granite is the orientation and grouping of the minerals, giving a rock marked by the presence of foliations or banding.
This foliation is an alternation of light beds and darker levels:
- Clear beds are made of acid crystals (quartz and feldspar).
- The dark beds are made of ferromagnesian minerals (biotite and amphibole).
This foliation is an alternation of light beds and darker levels:
- Clear beds are made of acid crystals (quartz and feldspar).
These beds are very distorted with many folds superimposed on the foliation.
► The real "Marble"
For the geologist, a marble is a metamorphic rock derived from a sedimentary rock (limestone or dolomite).
During the transformation process, the sedimentary structures are erased and the carbonate rock recrystallizes into a cluster of calcite crystals made of calcium carbonate (CaCO3).
This gives a non-grainy crystalline rock, softer (scratchable with a knife) and sensitive to hydrochloric acid.
Detrital minerals or oxides give marble and its veins various colors:
- The white color characterizes a pure rock, without impurity (ex: Carrara marble).
- The green color comes from serpentinite (mineral resulting from the alteration of peridotite). It is found in "Sea Green" marble which also has white veins of pure calcite.
- The red color of a marble comes from a high content of hematite (ferric mineral). Ex: The red marble of Minervois.
► Bibliographical sources
The Questions to validate "The Marbles of the 1st Avenue"
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.
- Question 0 : Take a picture of yourself or something that identifies you on First Avenue, without showing the viewing areas.
This photo will have to be sent to us with the answers or to be added to your log.
Observation point 1 : N 47° 36.200' W 122° 20.110'
Here you are on the first avenue at the intersection of Columbia Street, north-west side.
Observe the first meters of facing of the building forming the corner on the west side (Fado building).
- Question 1 : Describe the rock at the corner of the two streets. Is it real marble? If yes, say the name of this marble; if not what rock is it?
- Question 2 : What is its main color? Give the name of the mineral at the origin of this color.
Observation point 2 : N 47° 36.205' W 122° 20.091'
Cross the 1st avenue and observe the rock forming the facing of the building making the angle on the north-east side (Norton Building).
- Question 3 : Describe the rock covering the building at the corner of the two streets. Is it real marble? If yes, say the name of this marble; if not what rock is it?
Observation point 3 : N 47° 36.237' W 122° 20.121'
Go up the first avenue towards WP3 and observe the rock forming the first meter in height of the Exchange building (red areas of the WP3 photo).
- Question 4 : Describe the rock behind the red areas on the photo WP3. Is it real marble? If yes, say the name of this marble; if not what rock is it?
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.