← Geology syllabus

WalesGeology

G1: Rock Forming Processes

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

How do magmas form, evolve and produce the range of igneous rocks?

Partial melting of the mantle and crust, the controls on melting (temperature, pressure and water), magma series, and the evolution of magma by fractional crystallisation interpreted through Bowen's reaction series.
A focused WJEC and Eduqas A-Level Geology G1 answer on how magmas form by partial melting, the roles of temperature, pressure and water, the basalt-andesite-rhyolite series, and how fractional crystallisation governed by Bowen's reaction series evolves a magma and produces the range of igneous rocks.
14 min answer →

How do cooling rate and emplacement control igneous textures and forms?

The control of cooling rate on crystal size and texture (glassy, fine, coarse, porphyritic), and the recognition of intrusive forms (dykes, sills, batholiths, laccoliths) and extrusive forms (lava flows, pyroclastic deposits) with their contact relationships.
A focused WJEC and Eduqas A-Level Geology G1 answer on how cooling rate controls crystal size and igneous texture, the meaning of porphyritic and glassy textures, and how to recognise intrusive bodies (dykes, sills, batholiths, laccoliths) and extrusive forms by their geometry, grain size and contact relationships such as chilled margins and baked contacts.
13 min answer →

How do heat, pressure and fluids transform rocks in the solid state?

Contact, regional and dynamic metamorphism, the controls of temperature, pressure and fluids, the increase of grade and the use of index minerals and metamorphic facies, and the textures (slate, schist, gneiss, hornfels, marble, quartzite) they produce.
A focused WJEC and Eduqas A-Level Geology G1 answer on contact, regional and dynamic metamorphism, the controls of temperature, pressure and fluids, how grade increases, the use of index minerals and metamorphic facies to read pressure-temperature conditions, and the foliated and non-foliated textures (slate to gneiss, hornfels, marble, quartzite) that result.
14 min answer →

How do clastic, biogenic and chemical sediments form and turn into rock?

The formation of clastic, biogenic and chemical sedimentary rocks, the processes of diagenesis (compaction, cementation, recrystallisation), and the use of sedimentary structures, including those formed by infrequent processes such as turbidity currents, as evidence of conditions.
A focused WJEC and Eduqas A-Level Geology G1 answer on how clastic, biogenic and chemical sedimentary rocks form, the diagenetic processes that lithify and alter them, and how sedimentary structures, including graded bedding from turbidity currents, are read as scientific models of conditions that are hard to observe directly.
13 min answer →