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Gneiss Weather

A cache by Fingers Crossed Send Message to Owner Message this owner
Hidden : 06/03/2009
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Geocache Description:

This earthcache location will bring you to view an area of Georgian Bay's fabulous and distinct smooth granite rock shoreline. Parking is nearby so it is not necessary to park along the road.

There is a footpath that will lead you to the site or alternatively, you may walk along the shoulder for more level footing. However, the terrain at GZ can be tricky and will likely become slippery in certain weather conditions.

It is also located near a fast moving water source so keeping a close eye on children is a must.

During the precambrian era (500 million years ago) the Canadian Shield was formed ,caused by the convergence of two techtonic plates.This action forced the granite surface rocks into the interior of the earth where they melted, and rose close to the surface, cooling at a slow rate. The resulting rock is gneiss, an igneous rock.

  • Gneiss - Coarse-grained granular rock with alternating bands of light (quartz and feldspar) and dark (biotite and hornblende) minerals. Produced by high-grade metamorphic conditions.
  • Granite- Common intrusive igneous rock. It is coarse-grained and is composed of the mineral, feldspar, quartz and biotite and muscovite mica. It has high silica content and occurs only in continental crust. Granites are light-colored, usually in grays and pinks, their color being determined by the color of the feldspar in the granite. Darker granites and even green granite are known.
    Granite is very hard and dense. It can be readily cut into very large blocks and it takes an extremely high polish. Weathered granite, by comparison, crumbles easily. When granite is weathered and eroded, the feldspar and mica break down into clay minerals, leaving the very resistant quartz grains behind. Most beach sand is composed of quartz grains derived from granite.

At the posted coordinates you will discover a granite vein exposed within metamorphic rock Typically, the slower that magma cools the larger the crystal particles created will be. This vein is A great tactile example of Mother Nature at work.

While glacial erosion of the last ice age, 2.5 mllion years ago, has played a role, exposing and shaping the rock to it's current state, there are other ongoing factors to consider.

Physical or Mechanical weathering:

Thermal :
Extreme heat, from the sun’s rays to the hot summer temperatures, cause the rock to expand. Likewise colder temperatures cause these same rocks to contract. These movements alter the integrity of the granite causing stress and eventual breakdown.
Exfoliation or Unloading :
The overlying rock has put on tremendous pressure to the underlying rock. Once that pressure is released, the surface rocks expand and fracture parallel to the surface in flat sheets
Frost wedging :
Moisture captured in fissures and crevices freeze and thaw repeatedly fracturing the rock into angular pieces

Chemical weathering.

Dissolution changes rock formations by removing the minerals that are soluble. Some minerals dissolve in water and can be carried further downstream where they may be deposited as they precipitate or crystallize.
Certain rocks can ‘rust’. Iron bearing minerals weather and produce iron oxides. Other iron bearing silicates containing aluminum can also undergo oxidation and hydrolysis which forms iron oxides and clay materials.
Hydrolysis is the process that feldspar undergoes and is weathered to form clay. Nearly all the common rocks of the Earths crust will weather to form clay with the exception of quartz. (Clays make up nearly half the sedimentary rocks on Earth)

Biological Weathering

Lichen grow on the rock secreting an acid which dissolves the minerals in the rock leaving crevices. This facilitates the physical weathering mentioned above.
In addition to lichen created acids, other vegetation create acids as they decay along with animal carcasses.

In order to log this cache please answer the following questions via our profile: If you would like a reply to your answers, be sure to select the 'include your email address' option with your message.

1) How long is the prominent vein?

2) What kind of weathering has occurred at this spot to create this formation?

3) Why has this vein been left virtually untouched?

4) At N44 48.195 W79 43.351 is an additional geological feature. What does it look like to you?

5) What do you think caused this child sized feature?

Additional Hints (No hints available.)