This Gemstone Patio was placed to celebrate the Rockhound Gemboree, a annual event in Bancroft, which is world renowned for its various minerals, blue sodalite in particular. This patio is accessible from the public sidewalk and there is plenty of parking nearby. This earthcache may not be doable in winter depending on snow.
The Bancroft area is part of the billion year old pre-Cambrian Shield also known as the Canadian Shield. The rocks around Bancroft were part of a pre-cambrian mountain region. These rocks are a type called catazone, which is a deeply buried rock. Due to the repeated glacial erosions over thousands of years, the formerly buried rock is now at the surface for us to easily access.
In the image below, you can see the location of Bancroft on a long mountain chain, approximately 750 million years ago. (from dinosaurpictures.org)
Examples of minerals in the Bancroft area include:
Sodalite
Blueish coloured gemstone but may also come as grey, yellow, green or pink. Sodalite is named for its sodium content, and has been regularly mined in the Bancroft area, in particular the Princess Quarry since 1906.
Uranium
Mined starting in the 1950s with the boom in nuclear energy research and production. From 1956 to 1964, over 5 million kilograms of uranium oxide were produced.
Aplite
An ingneous rock similar to granite. These rocks are well known for the Aplite dykes of quartz and feldspar which streak through them.
Pegmatite
Similar to Aplite, this rock is known for its dykes. Unlike aplite which appears in smaller areas, Pegmatite can appear larger than a kilometer long! Pegmatite is also much coarser than fine-grained aplite.
Calcite
A very common crystal that is white or non-coloured, often appears a pink or reddish but can be found in a variety of other colours. Found in sedimentary rock such as limestone.
Nepheline
Igneous Rock composed of nepheline, albite and potash feldspar. These can be white, yellow, grey, green or reddish. This is an alkaline rock.
Gabbro
Dark coloured igneous rock. Very coarse grained. It has a similar chemical make-up to basalt, however cools more slowly when formed from magma.
Migmatite
A metamorphic rock with layers of pegmatitic or aplitic rock in it, which can appear as folds.
Questions - Please send me answers to the following:
1. Examine the sodalite in the patio, estimate the size of the largest and smallest specimens you see.
2. Besides sodalite, identify another mineral you see in the patio. Is it Pre-Cambrian?
3. Next to the street light base you will see a large black rock with a white line in it. What type of rock is this and what is the white band an example of?
Feel free to post a picture of yourself nearby with the plaque or your favourite rock!
Sources: http://www.geologyontario.mndm.gov.on.ca/mndmfiles/pub/data/imaging/GB03/GB03.pdf , Wikipedia