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Module 2: Foundations in geology - 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.

Why do minerals crystallise from a magma in a set order, and how does that change the magma?

Igneous processes: Bowen's reaction series as the order in which silicate minerals crystallise from a cooling magma; the discontinuous (olivine to biotite) and continuous (calcium-rich to sodium-rich plagioclase) branches; the use of the series to explain fractional crystallisation, magma differentiation and the resistance of minerals to weathering.
A focused answer to the OCR H414 dot point on Bowen's reaction series. Covers the discontinuous and continuous branches, the crystallisation order of silicate minerals, how fractional crystallisation drives magma differentiation from basic to acid compositions, and how the series predicts weathering resistance.
12 min answer →

What shapes do igneous bodies take underground and at the surface, and how do we recognise them?

Igneous bodies: the forms of intrusive igneous bodies (batholiths, dykes, sills and laccoliths) and their relationship to the country rock (concordant versus discordant); chilled margins, baked margins and contact metamorphic aureoles as evidence of intrusion; the recognition of extrusive forms (lava flows and their cross-cutting relationships) and the use of these relationships to establish relative age.
A focused answer to the OCR H414 dot point on igneous bodies. Covers batholiths, dykes, sills and laccoliths, concordant versus discordant intrusions, chilled and baked margins and contact aureoles as evidence of intrusion, and how cross-cutting relationships of dykes, sills and lava flows establish relative age.
12 min answer →

How are igneous rocks classified by composition and texture, and what do textures reveal about cooling?

Igneous rocks: classification by silica content (acid, intermediate, basic and ultrabasic) and by grain size (coarse-grained intrusive, fine-grained extrusive); the relationship between cooling rate and crystal size; igneous textures (phaneritic, aphanitic, porphyritic, glassy and vesicular) and what they show about the cooling history; naming common igneous rocks such as granite, gabbro, basalt and rhyolite.
A focused answer to the OCR H414 dot point on igneous rock classification. Covers acid, intermediate, basic and ultrabasic compositions, coarse versus fine grain size, the link between cooling rate and crystal size, the main textures (phaneritic, aphanitic, porphyritic, glassy, vesicular), and naming granite, gabbro, basalt and rhyolite.
12 min answer →

How are the silicate minerals built, and how do we identify the common rock-forming minerals?

Minerals and rocks: the structure of the silicate minerals based on the silica tetrahedron; the silicate groups (isolated, chain, sheet and framework silicates) and how the degree of polymerisation links to composition; the physical properties (colour, lustre, hardness, cleavage, fracture, streak, density and habit) used to identify the common rock-forming minerals quartz, feldspar, mica, olivine, pyroxene and amphibole in hand specimen.
A focused answer to the OCR H414 dot point on rock-forming minerals. Covers the silica tetrahedron, the isolated, chain, sheet and framework silicate groups, how polymerisation links to composition, and how to identify quartz, feldspar, mica, olivine, pyroxene and amphibole from physical properties in hand specimen.
13 min answer →