Geoscience Reference
In-Depth Information
bags come with write-on labels available from a variety of
suppliers. Check for rocks with sharp edges because they
tend to split the bag. If the rock has sharp edges either
round them by gently tapping them using the square end of
your hammer or carefully place the rock in a bag and wrap
over this with paper.
•
Aluminium foil:
This is useful for holding together very
fragile specimens such as mudstones. Wrap the foil around
the specimen immediately after extraction in a systematic
manner so that you are able to remove it sequentially in the
laboratory. Aluminium foil is best avoided if the samples
will be stored for any length of time as salts from the rock
tend to corrode the foil.
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•
Glue:
A strong glue suitable for metal or wood can be
used for sticking samples together. If you need to protect
fragile specimens such as shelly material within mudstone
or vertebrate teeth before shipping or transporting them
back, soak the sample for several hours in a 50:50
mixture of PVA glue and water. Then allow the specimen
to dry.
•
Marker pens:
Permanent marker pens provide a distinct
label. Note that wet, dusty or fi ne-grained dark coloured
rocks can be diffi cult to mark. It is worth carrying several
markers into the fi eld because they tend to wear out
quickly.
Specimens of fi ne-grained
rocks (mudstones and
siltstones) are often easier to
mark up with a tile scribe
and/or paper correction fl uid
because marker pen ink often
tends to be absorbed into the
rock.
13.2.2 Extraction of samples
Different rocks break in different ways, but skill and experience
enable the geologist to obtain the best samples. It is worth
spending some time working out where to extract the best
sample. Look for somewhere that is safe and easy to access and
where there is a piece jutting out that might easily be removed.
You should also consider the impact of extraction on the
environment and preferably choose a location that will not be
obvious. If you need just a small sample, tapping off the edge
of the bed with the fl at end of the hammer usually works. If
you need a larger sample look for areas where there is already
a line of weakness such as a bedding plane or joint. This can
often be widened and the rock weakened by hammering a cold
chisel into the joint or bedding plane and then using leverage
to extract the rock. For most fossils the rocks will need to be
split along the bedding plane. Some samples are hard to extract
and it may take a lot of forceful blows with the hammer over
time to weaken the rock. If you need a specifi c piece then use a
chisel and work carefully around the sample. You should
chisel far enough away from the specifi c area that you need
because there will always be some material lost close to where
