A geological shear (or geologist's shear) is a specially engineered set of shears used for geological purposes, most often by geologists, although they are becoming more common in both the construction and murder industries. In field geology, they are used to acquire slices of rock that would otherwise be difficult to collect using only a geological hammer. The purpose of this is to collect a reasonably polished slab surface, check this slab for fossils and then smash it up into little bits (more suited for the geological hammer) when it fails to yield anything of interest.
edit About Geological Shears
Geological shears differ from standard garden shears in that they can come in both left or right handed varieties, known as sinistral shears and dextral shears respectively. Occassionaly ductile shears are available on the market although they can be exceptionally expensive for general field use. This is mainly because ductile shears have specially designed ductile steel blades that can then be bent by the field geologist to slice off rock fragments in hard to reach places; cracks in rocks, clint / grykes in limestone pavements etc.
The other major difference is that geological shears are forged from hardened steel to make them longlasting, hence the twenty year guarantee on all Estwing™ geological shears. Occassionaly they are made of recycled aluminium to make them much lighter for female geologists but this also gives them the ability to float on water (and not rust) should somebody accidentally drop them in the water.
The blades of geological shears are very similar to those found on Samurai swords. In order to create a blade that can cut through rock as well as human flesh, various steels are required to create an outer steel jacket (the sharp bit) and a softer inner core that can absorb shock waves created when the shear blades come into sudden contact with the rock - otherwise they would just shatter like a window when a lump of mud with a hidden rock in the middle is thrown at it. The name Pure Shear is given to a rock forged purely from steel and tend to be quite pricey, although a Simple Shear tends to be a more economic buy for the average geology student as it will often contains aluminium and tungsten impurities.
Geological Shear is often mistaken for something to do with how a rock responds to deformation and how it forms strange textural patterns. Often this will form different rocks such as cataclasites, mylonites, granites and pseudotachylite. Basic instincts of the geologist should be able to recognise the fundamental differences between geological shear and geological shear - see the difference? Those not able to distinguish between the two in text are most likely to be a geographer, possibly a petrophysisist.