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Minerals and rocks

4 dot points across 4 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How do geologists identify a mineral from its physical properties?

Minerals are identified using physical properties: colour, crystal size, hardness (tested against fingernail, copper coin, steel and glass), cleavage and fracture, lustre, streak, and the reaction of carbonates with dilute hydrochloric acid; common minerals include quartz, feldspar, mica, calcite, halite, galena and haematite.
A focused answer to the Eduqas GCSE Geology statement on identifying minerals. Covers the physical properties used (colour, crystal size, hardness, cleavage and fracture, lustre, streak and the acid test) and the diagnostic features of quartz, feldspar, mica, calcite, halite, galena and haematite.
13 min answer →

How does cooling rate control the texture of an igneous rock?

Igneous rocks form by the crystallisation of magma or lava; cooling rate controls crystal size (slow cooling at depth gives coarse-grained intrusive rocks such as granite, fast cooling at the surface gives fine-grained extrusive rocks such as basalt); rocks are classified by crystal size and by silica content (felsic, intermediate, mafic); minerals also crystallise from hydrothermal fluids to form veins.
A focused answer to the Eduqas GCSE Geology statement on igneous rocks. Covers how magma and lava crystallise, how cooling rate controls crystal size (intrusive granite versus extrusive basalt), classification by silica content (felsic to mafic), and the crystallisation of minerals from hydrothermal fluids in veins.
14 min answer →

How do heat and pressure change one rock into a metamorphic rock?

Metamorphic rocks form by recrystallisation of existing rocks in the solid state under heat and pressure, without melting; contact metamorphism (heat from an intrusion) produces non-foliated rocks such as metaquartzite and marble; regional metamorphism (heat and directed pressure over a wide area) produces foliated rocks such as slate and schist; protolith and conditions determine the product.
A focused answer to the Eduqas GCSE Geology statement on metamorphic rocks. Covers solid-state recrystallisation under heat and pressure, the difference between contact metamorphism (non-foliated metaquartzite and marble) and regional metamorphism (foliated slate and schist), foliation, and how the protolith and conditions set the product.
13 min answer →

How do sedimentary rocks and their fossils record the environment in which they formed?

Sedimentary rocks form by weathering, erosion, transport, deposition, and lithification (compaction and cementation); they are classified as clastic (conglomerate, breccia, sandstone, shale), biological (limestone) or chemical (evaporites); grain size, shape, sorting, sedimentary structures and fossil content are used to interpret the depositional environment; fossils form by preservation of hard parts and record past life.
A focused answer to the Eduqas GCSE Geology statement on sedimentary rocks. Covers weathering, transport, deposition and lithification, the clastic, biological and chemical classes (conglomerate, sandstone, shale, limestone, evaporites), reading the depositional environment from grain size, sorting and structures, and how fossils form and what they record.
14 min answer →