SCIENCE · INVESTIGATE AND EXPLAIN

Explain residual melt enrichment with a closed material budget

Cooling magma can contain crystals and liquid simultaneously. In Bowen’s reaction framework, early minerals can react with remaining liquid as conditions change; plagioclase composition can also evolve. A sequence is not a promise that every magma produces every mineral: initial composition, pressure, water and reaction time matter.

Learning outcome: Compare removal at silica fractions 0.3 and 0.5 with the same mass. Then vary removed mass while holding composition fixed. Close both total and silica budgets and identify the setting where residual composition is unchanged.

Starting recap

Separate observation, material inventory, process model and historical inference. State units and the evidence that could reject a proposed explanation.

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Try

Remove 20 kg crystals at silica fraction 0.4: 8 kg silica leaves, 42 kg remains in 80 kg liquid and the residual fraction is 0.525. Recombining both fractions restores 50 kg silica in 100 kg total.

Open the experiment

Predict

Can residual silica fraction rise while residual silica mass falls?

Your prediction and reason

Experiment

Compare removal at silica fractions 0.3 and 0.5 with the same mass. Then vary removed mass while holding composition fixed. Close both total and silica budgets and identify the setting where residual composition is unchanged.

Close a finite crystal-removal silica budget

Worked teaching model · synthetic values · Original 100 kg magma with50 kg SiO₂-equivalent. Remove specified crystals once, retain all other material in liquid; no new input, volatile loss or reaction after removal. Remaining liquid composition=(50−mass×crystal fraction)/(100−mass). This is bookkeeping, not a calibrated phase-equilibrium or Rayleigh model.

Removed crystal mass: 20 kg Silica mass fraction of removed crystals: 0.4 fraction

Reset keeps your prediction, captures and practice history.

Removing a silica-poorer solid can enrich the remaining liquid without adding silica.

Crystals left in contact can react with liquid; physically separated crystals follow a different history. Real mineral stability and melt composition need independent phase evidence. The bulk initial system remains50% silica by mass when both fractions are counted.

Complete quantities under the stated assumptions
Quantity	Value	Unit
Initial silica-equivalent mass	50	kg
Removed silica-equivalent mass	8	kg
Residual silica-equivalent mass	42	kg
Residual total mass	80	kg
Residual silica mass fraction	0.5250000	fraction
Removed plus residual total	100	kg

Retain the prediction and settings before comparing explanations. Replayed supplied observations are not new specimens, independent field samples or practical certification.

Removing a silica-poorer solid can enrich the remaining liquid without adding silica.

Observation to attach to a capture

Captures preserve recipes and replay their calculated results. They are synthetic model evidence, not physical measurements.

Understand

1. Define the geological question

2. Build the mechanism and evidence ledger

Physical separation of crystals changes the composition of the remaining liquid. This process differs from leaving crystals available to react. The original model starts with 100 kg magma containing 50 kg SiO₂-equivalent. A single removed crystal fraction has specified total mass M and silica mass fraction c.

The removed silica mass is Mc, so residual silica is 50−Mc and residual total mass 100−M. Their ratio gives residual silica fraction. If the removed material is poorer in silica than the original magma, the residual fraction rises even though its absolute silica mass falls.

This finite mass balance does not predict which phase crystallizes, at what temperature, or how trace elements partition continuously. Those require additional thermodynamic or partition information. Reporting both absolute mass and composition prevents the mistaken inference that enrichment created matter.

3. Reconstruct a worked example

Remove 20 kg crystals at silica fraction 0.4: 8 kg silica leaves, 42 kg remains in 80 kg liquid and the residual fraction is 0.525. Recombining both fractions restores 50 kg silica in 100 kg total.

4. Predict and investigate

Predict first: Can residual silica fraction rise while residual silica mass falls?

5. Test a changed case

Apply the mechanism to a changed case

Remove 40 kg crystals with silica fraction 0.3. Find residual silica mass, total mass and fraction.

Retain the calculation, evidence and assumptions before opening public feedback.

Compare a worked response

Removed silica is 12 kg; residual silica 38 kg in 60 kg liquid gives 0.6333. Its silica mass fell while its silica fraction rose.

6. Retain evidence and its limits

Keep the first prediction, complete ledger, changed case and rejected alternative in the lesson notebook. Supplied observations and bounded CPU models are not actual specimen handling, fieldwork or independently assessed competence. Record source purpose and uncertainty rather than treating public feedback as independent reasoning.

Mechanism and classification reference, checked 30 October 2026. Original teaching prose, numerical packets and questions; no source illustration or exercise is copied.

Apply

Public practice checks a specific claim. It does not establish independent mastery.

Remove 40 kg crystals with silica fraction 0.3. Find residual silica mass, total mass and fraction.

Your explanation and limitations

Continue

Completion requires a saved prediction, at least one capture and a reflection. Presence checks do not grade your reasoning.

Skipping retains experiments and awards no mastery.

Previous: Separate igneous texture, mineral modes and mass composition Next: Distinguish chemical transformation from mechanical fragmentation

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