Geoscience Reference
In-Depth Information
•
Hue
: There are 10 major hues defi ned by the Munsell
colour system. These are represented on the sphere by
division of the sphere into 10 'slices' or segments (Figure
2.17a). Each slice is further subdivided into 10 numbered
slices. The number 5 marks the centre of the hue and 10
the boundary with another hue.
•
Chroma
: This is the degree of saturation of the hue with
respect to the equivalent grey. This is defi ned on the sphere
by how far it lies between the centre of the sphere and the
circumference (Figure 2.17a and c).
2
1
2
The Munsell colour value is given in numbers as: Hue Value/
Chroma. So, for instance, 5R 4/6 refers to a hue of 5R, a value
of 4 and a chroma of 6.
3
2.7 Hammer, chisels and other hardware
A geological hammer is necessary for most geological
fi eldwork, both for the collection of samples and, where
necessary, to create fresh surfaces so that the rock and the
minerals within it can be described (Figure 2.18). Having said
this it is perfectly possible to do a lot of geological fi eldwork
without a hammer provided samples are not required. Rocks
that are exposed in sea-cliffs and along foreshores, in new
trenches or in road cuts often do not need hammering and
indeed the slightly weathered or wave washed surface is often
as good as, if not better than, a hammered surface. For
sedimentary rocks a 1 lb (
c.
0.5 kg) hammer is often suffi cient.
For igneous, metamorphic and hard or well-cemented
sedimentary rocks a 2 lb (
c.
1 kg) or even a sledge-hammer may
be necessary if good quality and/or large samples are required.
However, a good chisel or pick hammer can be used to exploit
planes of weakness (joints, bedding planes, foliation, vein
margins) and extract samples from tougher rock types (Section
13.2.2). Matters of conservation should always be considered
(Section 2.12).
4
5
6
7
8
For safety reasons it is important to use a geological hammer
rather than one designed for other materials such as wood or
metal. This is because to hammer rocks you need a head
that is robustly mounted on to the hammer shaft, made of a
suitable grade of steel that will not splinter and is of an
appropriate ergonomic design. Brick and stone hammers can be
used if a specifi c geological hammer is not available. Other
features to consider when purchasing a hammer are the type of
head that is most suitable for your use and whether it feels
comfortable when you use it. All geological hammers have one
fl at face: the other end is either a chisel or pick (Figure 2.18).
The chisel end is useful for splitting rocks apart although it is
Figure 2.18
Some of the
different geological hammers and
cold chisels available on the
market. (1) Estwing pick end
hammer, (2) Estwing chisel end
hammer, (3) cold chisel with hand
guard, (4 and 5) 2.5 lb and 1 lb
geological hammers with fi breglass
shafts, (6) pencil chisel, (7) tile
scribe and (8) 3 lb lump hammer.
