Rock formation and changing pathways

A rock group describes an origin

Texture describes grain size, shape and arrangement. Composition describes the materials present. Formation describes the processes through which the rock developed

Igneous, sedimentary and metamorphic are major rock groups distinguished by formation. One colour, a mineral name or the size of a whole specimen cannot establish the complete history

Crystals can grow from molten material, from dissolved material in water, or during changes within solid rock. Finding crystals is therefore not by itself proof that the whole specimen once melted

The next model supplies a view of grains, not a geological history. Enlarging that view changes what is displayed, not how the rock formed

Predict what a closer view can establish, then compare Whole patch with Centre enlarged for this fixed Model C. Follow the same central grains and the represented scale. Shading separates grains, not identified minerals; the control neither heats the sample nor runs a formation process

What can changing the view establish here?

Cooling from molten rock

Igneous rock forms when molten rock cools and solidifies. Molten rock below Earth's surface is called magma; molten rock at the surface is called lava

As many melts cool, mineral crystals grow from the molten material. Under otherwise comparable conditions, slower cooling gives crystals more time to grow and commonly produces larger crystals

Rapid cooling commonly produces small crystals. Very rapid cooling can form natural glass without an ordered crystal structure, so not every igneous rock has visible crystals

A growing crystal contains an increasing ordered collection of particles. It is not one individual particle becoming larger

Classify a complete cooling history

A supplied history records molten rock beneath Earth's surface cooling and becoming solid. Crystals grow from the molten material as it solidifies

Name the major rock group and explain which part of this supplied history establishes its origin

The history starts with molten rock and ends with solid rock

That cooling and solidification route forms igneous rock; the crystal evidence fits the recorded process

Connect cooling with crystal growth

From exposed rock to deposited sediment

Weathering breaks down or changes exposed rock in place. Mechanical weathering can break rock into fragments without moving them away

Erosion removes material, and transport carries it elsewhere by moving water, wind, ice or gravity. A fragment being carried is not the same event as its first breakdown

Deposition occurs when transported material settles or is left behind. Deposited fragments and other loose material are sediment, not automatically solid sedimentary rock

Uplift raises rock towards the surface. Removal of overlying material by erosion can expose rocks that originally formed below ground

Name each recorded surface process

Turn loose sediment into rock

Sedimentary rock can form when deposited sediment is buried, compacted and cemented. Burial adds overlying material that presses grains closer together, reducing pore spaces between them

Compaction is squeezing the sediment. Cementation occurs when minerals grow from water in the gaps and bind neighbouring grains. Neither process requires all the grains to melt

Layers can record changes in deposited grain size or composition. Their interpretation still needs context; a visible stripe is not automatically proof of a particular environment or age

Use the sediment's complete history

Distinguish squeezing from binding

Sedimentary does not always mean broken fragments

Some sedimentary rocks form when dissolved mineral material becomes solid crystals and accumulates from water. Evaporation can leave mineral deposits; this is not solidification of molten rock

Other sedimentary materials accumulate from living things, such as shell fragments or plant remains. Coal contains altered plant-derived material and is not simply a collection of mineral crystals

Use the supplied formation record. A mineral crystal or an organic constituent does not by itself replace that record

Follow mineral material from solution

Change an existing rock while it stays solid

Metamorphic rock forms when an existing rock is altered by heat, pressure or related geological conditions mainly while it remains solid. Its minerals can grow or reorganise and its texture can change

The earlier rock can be igneous, sedimentary or already metamorphic. Heat does not automatically mean melting, and pressure here concerns forces acting on the buried rock

If material melts and later cools into solid rock, that later solidification forms igneous rock. Distinguish the solid-state change from the separate molten stage

Examples include limestone changing to marble and shale changing to slate under suitable conditions. A name match is not a substitute for identifying evidence of that transformation

Keep the solid state in the explanation

Separate two successive histories

The rock cycle is not a fixed timetable

The rock cycle connects possible transformations of Earth materials. It has no single required starting point or order through every rock group

An igneous rock might become sediment through weathering, or become metamorphic without an intervening sedimentary stage. A rock can also remain in one condition for a very long time

The timescales differ. A storm can transport and deposit sediment quickly, while later burial and rock formation can take much longer. One event's duration is not the duration of the complete history

Compare two possible routes

Keep each process on its own timescale

Read traces of a history

Fossils are preserved evidence of earlier life, including body remains and traces such as tracks or burrows. They often occur in sedimentary rocks

A reliable fossil identification and its geological context can help reconstruct an environment or order of events. Appearance alone is not a verified fossil identification

A fossil does not automatically give an exact numerical age, and its presence does not exclude every later change. Use the dating and context information actually supplied

Use a verified fossil report

Avoid a texture-only origin claim

Construct two complete material pathways

Written and diagram task, not automatically marked

History A starts with buried igneous rock. Uplift and removal of overlying material expose it. It breaks into fragments, water removes and carries them, they settle, and later burial and mineral binding make solid rock

History B starts with another igneous rock. Heat and pressure change it while solid. Later it melts, and the melt cools and solidifies

Before reading the model, draw a separate arrow pathway for each history, labelling the material or rock group at each stage and the process on each arrow. Explain where A and B differ, which stages involve melting and why neither history supplies an exact age

Check material, process and evidence separately

A: buried igneous rock → uplift and removal of overlying material → exposed igneous rock → weathering → fragments → erosion and transport → moving fragments → deposition → sediment → burial, compaction and cementation → sedimentary rock

B: igneous rock → solid-state change under heat and pressure → metamorphic rock → melting → molten material → cooling and solidification → new igneous rock

A does not record melting; B does, after the metamorphic stage. The different routes show that rocks need not visit all groups in one fixed order

The ordered histories identify processes but supply no numerical dating measurements. Neither the diagrams nor the rock-group names establish an exact age

Review origin, process and limits

Use a formation history to distinguish cooling of molten rock, accumulation and binding of sediment, and alteration of existing solid rock

Keep weathering, erosion, transport, deposition, compaction and cementation distinct. Crystals can grow in several settings, and heating need not mean melting

Rock-cycle pathways and timescales vary. Combine texture, composition, fossils and context without inventing an exact origin, date or compulsory route from one observation