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Rocks, Rocks, Rocks!!!
Rock is the foundation of the surface of the
Earth. We live on it, mine it for useful materials,
make roads with it, grow food in it and generally
depend on it for many things. In British
Columbia there are very few places where you
don’t see rocks and much of our beautiful
scenery depends on interesting rock
formations. Some British
Columbia rocks are as
old as 2 – 2.5 billion years
and others are forming
right now.
Where, oh
where are these
pebbles from?
Pebbles and sand form when rock is broken down by
surface processes such as rain, freeze/thaw, heating and
biological activity. These broken up particles of rock are then
moved by gravity, water, wind or ice.
If the pebbles come from the surrounding rocks, they will look
the same and be the same colour. Around our beaches,
many of the pebbles are eroded out of glacial
deposits in the sea cliffs. These glacial
deposits were dropped by retreating
glaciers and ice sheets and contain
all the rock fragments, sand
and clay that the glacier
carried. Pebbles may also be
transported to the coast by
rivers.
Some of the pebbles on
our beaches have come a
long way. For example,
many of the granite and
granodiorite pebbles
we see around southern
Vancouver Island come
from the Coast Mountains.
While being transported by rivers or waves, the
broken rock fragments get rounder and smoother.
Even very angular debris that was carried
and deposited by ice, once it is eroded from
old glacial deposits and moved around by
waves at the beach, will become rounder.
Typically the further a piece of rock has
been carried and the more it has been
washed about, the smaller, rounder and
smoother it will be.
There are 3
different groups
of rocks
Typical minerals in igneous rocks are quartz – glassy; feldspar
– white, creamy, pink or grey; mica – black and flat; and
hornblende or pyroxene – greenish black.
When deciding if a rock is igneous look for:• Interlocking crystals of different minerals
often creating a speckled look
• Generally not layered or banded
• Hard and heavy
flowerstone
large crystals, often feldspar, in
a fine grained igneous rock
pink, white
black
grey
RHYOLITE (V)
GRANODIORITE (I)
the darker parts are
xenoliths, fragments of
the surrounding rock
that were incorporated
into the magma when it
intruded
2 Rock and Roll
or Sedimentary Rocks
SANDSTONE
Sedimentary rocks form at the Earth’s surface – no great heat
or pressure here! They are made of weathered and eroded
pieces of preexisting rocks which ended up being dropped or
deposited by wind, water or ice. When these sediments were
buried by more layers of sand, gravel or mud, the fragments
were cemented together and hardened or lithified (turned into
rock) to produce sedimentary rocks. Then, when they were
exposed again at the Earth’s surface, weathering and erosion
produced a whole new round of pebbles. Some sedimentary
rocks form from the remains of organisms such as corals and
shells e.g. limestone, or plants e.g. coal.
pink
GRANITE (I)
1 Magma Moments
or Igneous Rocks
Igneous rocks form when molten rock or magma cools. The
magma can cool quickly at the surface in volcanoes or lava
flows, forming Volcanic igneous rocks (V). Magma may
push into cracks deep inside the earth and cool very slowly,
forming Plutonic or Intrusive igneous rocks (I). The longer
the magma has to cool, the bigger will be the crystals
that grow from the magma. Volcanoes will
generally produce igneous rocks, like
basalt, with very small or invisible
crystals. On the other hand, magma
cooling slowly below the surface,
will produce igneous rocks
like granite, with large, visible
interlocking crystals.
The colour of an igneous rock
depends on the composition of
the magma. If the molten rock
is full of elements such as iron
and magnesium, the igneous
rock will be dark in colour. If the
magma contains more silica and
aluminium, lighter coloured igneous
rocks will form.
PORPHYRY (I OR V)
Vesicular basalt
(cavities that were filled with gas
as the magma cooled)
DIORITE (I)
When deciding if a rock is sedimentary look for:
• Rounded grains that show evidence of having been
transported by water or wind
• Fossils
• Layers, often of slightly different grain sizes
• Sedimentary rocks are often softer than either igneous or
metamorphic rocks
CONGLOMERATE
from sand
Acknowledgements
FOSSILIFEROUS SANDSTONE
The development of this guide was funded by a $2,000 grant from
the Canadian Geological Foundation.
Thanks to Ken Josephson for photographing
the pebbles and for creatively laying out the
pebble chart. Thanks to Karen Drysdale
for supplying some of the pebbles and for
sharing her enthusiasm for ‘time spent at the
beach’. Nick Massey proofread and provided
helpful comments on the text.
from gravel
Thanks Pete, Connor and Allie for your
support and for sharing in the journey.
Eileen Van der Flier-Keller
BASALT (V)
Basalt with
amygdules
(gas cavities filled
with minerals)
coarse gabbro
GABBRO (I)
SANDSTONE
Basalt
with ripples
To order copies of the guide contact:
c/o SEOS, University of Victoria,
PO Box 3055, Victoria, V8W 3P6
250-472-4019
DALLASITE (V)
BRECCIA
gabbro
ISBN 0-9738558-0-0
VOLCANIC BRECCIA (V)
MUDSTONE
3 Roughed-up Rocks
or Metamorphic Rocks
COAL
Black mudstone
Metamorphic rocks are formed when preexisting rocks are
changed (or metamorphosed) by heat and pressure deep in
the Earth. As a result new minerals such as green chlorite,
grey or black mica, or red garnet grow. The minerals in
metamorphic rocks are often aligned, giving the rock surfaces
a shiny, flattish look. The minerals also often form bands of
different colours e.g. in gneiss.
Mudstone with fossil
Laminated
mudstone
glassy,
layered
JASPER
from sandstone
QUARTZ VEINS
Where to go from here?
Join a local rockhound group
Check out books or field guides to rocks
and minerals
 Visit a museum
 Look for Earth Day activities at your
local university


GARNET SCHIST
Now you know ...
that rocks and minerals can tell interesting stories
about earth’s history.
When deciding if a rock is metamorphic look for:
• Minerals that are aligned, making flat shiny surfaces
• Layers of light and dark interlocking crystals
• Folding of layers may be visible
• These rocks are often harder than their parent rocks
CHERT
QUARTZITE
MICA SCHIST
MARBLE
But! Did you know that ...
from limestone
HORNBLENDE SCHIST
GRANITE GNEISS
FAULTS IN MUDSTONE
EPIDOTE
GRANITE
Some of the pebbles you will find on the beach are not rocks
at all, but are made of one mineral. Minerals are the building
blocks of rocks. A common example of a mineral is quartz.
Milky white, non-grainy, even pebbles are often pieces of
quartz veins that have been broken off and smoothed just like
the rock pebbles.
QUARTZITE
SANDSTONE
LIMESTONE
our building and homes are full of rock and
minerals! Quartz is used to make glass, gypsum is the main
ingredient in drywall, bricks are hardened clay, and concrete
is a mixture of limestone with sand and gravel. Not to mention
the granite, slate, marble and other rocks that make floors,
countertops, roofs, and sculptures.
Other Neat Stuff
PHYLLITE
CONCRETION
may contain a fossil
metals are used in the wierdest ways! Zinc (from
sphalerite) is used in antiseptic ointments, dandruff shampoo,
deodorant, dry batteries, textiles, wood preservatives,
cosmetics, brass, glues, printing inks, TV screens and
luminous dials on watches!
BLACK SAND
contains magnetite
SLATE
GNEISS
CONCRETE
Human made debris
QUARTZ
folded
FOSSILIFEROUS LIMESTONE
we eat minerals! How about salt to flavour dinner, or
calcium carbonate (calcite) which is used in making bread,
cookies, icecream, candy and toothpaste? Or gypsum - it’s
used as a filler in beer, spagetti, and vitamins, as a coagulant
in tofu, and in enriched flour, baking powder and canned
veggies.
BRICK
Mica is magnificent! Mica is used in paint, plastic, rubber,
rocket propellants, wallpaper, telephones, lasers, guided
missiles, explosives, heating elements in toasters and irons,
Christmas ornaments and artificial snow. Wow!