Just in time for International Earthcache Day 2021 and the new Earthcache Souvenir for Earthcache finds on on Saturday, October 9, or Sunday, October 10, 2021.
This is not your usual type of geocache. For one thing, there is no physical geocache for you to find. Rather, this is a special type of virtual cache known as an EarthCache.
An EarthCache teaches an earth science lesson. The cache page must include logging tasks that help teach the same lesson. Geocachers must complete the tasks before they log the EarthCache as found.
For more information on EarthCaches, see the Geological Society of America's website.
FINDING THIS EARTHCACHE
The given coordinates take you to the front entrance to the Wisconsin Gas Building, 626 E. Wisconsin Avenue. This Earthcache focuses on the large blocks of Morton Gneiss (sometimes called Rainbow Granite) and of Gabbros (sometimes called Black Granite) that cover much of the exterior of the first two floors of the building.
In order to get credit for finding the cache, it is not enough to log it below. You also must complete the following logging tasks based on the information provided and your observations at the given coordinates. Message or EMAIL your answers to the Cache Owner. Except where indicated, DO NOT place your answers in your log entry!!!
The difficulty rating is based on the thought and number of logging tasks required to log this Earthcache. Perfection is not required! However, at least a good faith attempt to fulfill the logging requirements is expected and would be sufficient.
Logging Tasks
Please note: All SEVEN mandatory logging tasks must be completed in order to claim the Find:
Information to be sent to CO by message or Email:
1. What type of rock is Gneiss - Igneous (rock formed when liquid magma cools), Sedimentary (rock formed when sediment is compressed and cemented together), or Metamorphic (existing rock that has been modified by heat, pressure, and/or chemical processes)? What about its creation makes you think so?
2. What colors do you see in the Gneiss on the building? What minerals do you believe created each of those colors?
3. What type of rock is Gabbro - Igneous, Sedimentary, or Metamorphic? What about its creation makes you think so?
4. Examine one of the Gabbro slabs at the base of the building. Estimate what percentage of the total is made up of each of the following minerals: pyroxene, plagioclase, olivine (for this, we will assume there is no amphibole). Why do you think so?
5. Based on your observations of the building and the information provided below, identify three differences between the Gneiss and the Gabbro on the building. These can be their appearance, their mineral composition, the size or color of their crystals, how they were created, their relative “age,” etc.
6. Measure or estimate how thick the Gneiss slabs are on the building. Then do the same for the Gabbro.
Information to be included with your online log:
7. To prove that you were actually at the location of the Earthcache, post a photo with your log of you, members of your team, or an item of personal property such as your gps at the main double-door entrance. Try not to include the Gneiss or Gabbros siding slabs in the photo.
Optional Non-Earth Science Information to include with your online log:
At your option, you may identify in your log the time when you visited the building, whether the flame at the top of the building was lit when you visited, the color of the flame, and the weather at that time. You may even include a photo of the flame.
THE WISCONSIN GAS BUILDING
The Wisconsin Gas Building is a classic stepped Art Deco tower located at 626 East Wisconsin Avenue. It was designed by architects Eschweiler & Eschweiler and completed in 1930. The 20-story building originally served as headquarters for the Milwaukee Gas Light Company.
The building’s design is distinguished by its prominent bronze sunburst motif, the graduated setbacks of the upper floors, and the use of differing materials on the exterior, fading from dark – Gabbros (“Black Granite”) and Morton Gneiss (“Rainbow Granite”) – on the first two floors to light – Cream City Brick – toward the top. All of this lends the impression of a much larger structure.
A weather beacon shaped as a natural gas flame 21 feet high and weighing 4 tons was added to the top of the Wisconsin Gas Building in 1956. It indicates the weather forecast by its color and flicker.
The traditional Neon lights in the beacon were limited to three colors: Red, Gold, and Blue. A rhyme helps to remember the colors’ meanings:
When the flame is red, it's warm weather ahead.
When the flame is gold, watch out for cold.
When the flame is blue, there's no change in view.
When there's a flickering flame, expect snow or rain!
With the change to an LED lighting system in 2013, the flame can now produce any of millions of colors for special occasions.
MORTON GNEISS
Morton gneiss (pronounced “nice”) is named for the town in Minnesota where it has been quarried since about 1884. It is one of the oldest stones ever dated: about 3.5 billion years old.
The following information comes from an article by Paul Nelson on Morton gneiss on the Mnopedia website, which claims to be “[a] resource for reliable information about significant people, places, events, and things in Minnesota history.”
The rock known as Morton gneiss started out as a gray granite, formed about 3.5 billion years ago deep beneath the surface of the Earth. Molten rock cooled slowly, forming grains (granite comes from granum, the Latin word for grain) of crystallized minerals.
About a billion years later, two fragments of the Earth’s crust collided at the future location of southwestern Minnesota, subjecting the granite to heat and pressure. These forces melted it once again and allowed intrusions of molten pink granite. The two granites folded and twisted; when they hardened (very slowly), the twists and folds remained. Eight hundred million years later, another geologic heating event added additional color and texture.
When cut and polished, Morton gneiss shows bands and swirls of black, pink, and gray, with white flecks, that sometimes look like galaxies and nebulae floating in the cosmos. The rock’s colors come from quartz (white), pink feldspar (pink), gray feldspar (gray), and biotite and amphibole (black).
About one hundred million years ago, geologic forces slowly pushed Morton gneiss to the Earth’s surface. The glaciers that advanced and retreated across southwestern Minnesota between two million and 12,000 years ago covered the rock with hundreds of feet of soil and rock.
When the last glaciers began receding about 12,000 years ago, a vast body of water known as Lake Agassiz formed in southern Canada, Minnesota, and North Dakota. When that water drained to the south, forming the River Warren, it carved out the Minnesota River valley. This powerful flow washed away hundreds of feet of glacial deposits and exposed some of the Morton gneiss.
Though Morton gneiss is as tough and durable as granite, it has rarely been used as a building stone. Architects have used it mainly in the lower floors of large buildings for its visual appeal. It enjoyed its greatest popularity during the Art Deco era of the 1920s and 1930s.
Although sometimes called "Rainbow Granite," it is not technically a granite, which is a type of igneous rock.
GABBRO
Gabbro is a coarse-grained, chrystaline rock formed from the slow cooling of magnesium-rich and iron-rich magma deep beneath the Earth's surface. Much of the Earth's oceanic crust is made of gabbro, formed at mid-ocean ridges.
Gabbro is dense, greenish or dark-colored, consisting primarily of pyroxene (up to 70%), which provides much of its dark color, plagioclase (a clear or white feldspar, up to 50%), and minor amounts of amphibole (generally, though not always dark) and olivine (green). The darker minerals are high in magnesium and ferric oxides, and their presence gives Gabbro its characteristic dark color.
Although Gabbro used for ornamental facing stones and kitchen countertops is sometimes known as “Black Granite,” true granite contains substantial quantities of quartz (>20%), while Gabbro contains little if any quartz.