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Activity

Granite minerals

Summary: 
Students look closely at black granite (granodiorite) from the beach and find out what minerals are in it. They can study it in the context of other beach rocks, or in a lesson on crystals.
Science content (2016 curriculum): 
Chemistry: Crystals (7)
Earth/Space: Rock cycle, Earth Materials, Natural resources (5)
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Materials: 
  • black granite (granodiorite), or other kind of common granite
  • optional: other beach rocks
  • magnifiers
  • flashlights/bike lights/white holiday lights
  • pencil and paper for drawing
  • optional: each of the minerals in granite - mica, feldspar, quartz
  • optional: image of a cross section of the earth, showing the liquid rocks inside
  • optional: samples of volcanic rock e.g. basalt, pumice, obsidian
Procedure: 

Go on a beach walk to find granite, or bring it into the classroom. Students will have seen it frequently, but have not taken notice.

Students can sort granite from other rocks by its speckled appearance. In Vancouver, a black rock is likely to be basalt (igneous rock), and a rough light brown rock is likely to be sandstone (sedimentary rock). Smaller pieces of quartz may also be found - clear or yellowish and more shiny.

Use magnifiers to look at the black granite closely:
Students can draw the outline of their black granite, then choose one part of it to draw in detail. Use the magnifier to find the different colours in it. (A pencil is sufficient to show the blacks, greys and whites).

For a lesson on crystals, students can find the flat faces of crystals of the minerals in granite.

Find the different minerals in the black granite:
Ask students to say what colours they found. Some may have found stains of green algae across the rock. Some may have found specks of other colours, but the majority of the rock is three colours: black, grey/pink/yellow, and white.
These three colours are the three minerals that make up black granite. In this rock they are easily distinguishable (the "grain size" is large).
(Optional: show other rocks where the minerals are distinguishable).

Hold a flashlight up to your black granite and look for the sparkles on the black mineral.
The shiny flat crystals are mica - mostly black mica in our rocks, but sometimes mica is white. Show students a large mica sample, if available. Label your black granite drawing showing where the mica is.
The pink/yellow is feldspar. Show a feldspar sample if available.
The white is quartz. Students may have heard of quartz. Quartz is very common and you might find big chunks of it on the beach. Show a large quartz crystal if available. Quartz can come in other colours and makes beautiful crystals - show amethyst if available.

Optional: discussion on how the black granite was made.
The black granite we are holding was once deep inside the earth.
It is so hot in there that the rocks have melted and all the minerals are liquid (show picture of a cross section of the earth). Imagine how hot it needs to be to melt rocks! As the minerals move away from the centre they cool down, and this granite was made when mica, feldspar and quartz grow their individual crystals.
Some rocks that melt inside the earth are still molten when they come to the surface: volcanoes.
Show volcano rocks - basalt (common here), pumice and obsidian. Can see gas bubbles in them.

Notes: 

granodiorite and quartz diorite are beach rocks (check if these are black granite)

Grades taught: 
Gr 1
Gr 2
Gr 3
Gr 4
Gr 5
Gr 6
Gr 7
Teacher: 
Alane Lublow
Heather Wallace
Ingrid
Nellie Wong
Scott Malin
Teaching site: 
Bayview Elementary Science Club
General Gordon Elementary Science Club
ingridscience afterschool
Tyee Elementary
Activity originally developed and delivered: 

Gordon Elementary Science Club