Laboratory techniques (thin section analysis, analytical tests, and fossil identification)

Laboratory techniques

Thin sections are slices of rock that have been ground down to a thickness of 30 micrometres. They show the mineral composition and structure of the rock and can be analysed under a microscope.
Petrographic microscopes are used to analyse thin sections. They allow observation of the minerals’ optical properties like colour, pleochroism, relief, and cleavage.
Familiarise yourself with features such as extinction angles, birefringence colours and twin laws, as distinguishing these properties can help to identify mineral types and rock fabrics.
Understand how to interpret thin sections, recognising textures and features typical of igneous, metamorphic, and sedimentary rocks.

Analytical tests such as the streak test, hardness test, acid test, and specific gravity test are used to identify minerals.
The streak test consists of crushing a mineral to powder to observe the colour of its powder, which can be different to the colour of the whole mineral.
The hardness test evaluates a mineral’s resistance to scratching. The Mohs Hardness scale, which ranges from 1 (talc) to 10 (diamond), is commonly used for comparison.
The acid test helps identify minerals containing carbonate. Dropping dilute hydrochloric acid will cause carbonates to fizz or effervesce.
The specific gravity test gauges a mineral’s density and can be used to distinguish between minerals of similar appearance.

Fossils provide evidence of past life and are often crucial for dating rocks and reconstructing past environments in the geological record.
Characteristics utilised in identifying fossils include shape, size, symmetry, and internal structures.
In order to identify a fossil, it is important to understand its morphological features and to compare it against a fossil reference guide.
Be aware of the principle of fossil succession, which implies that fossil species succeed each other in a specific, recognisable order. This knowledge is integral to biological stratigraphy.
Grasp the concept of biozones: time-stratigraphic units defined by the first and last appearance of a particular fossil species or group. These are vital for correlation and age determination.