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Earth's Systems / Biological processes / Terrestrial ecosystem functioning / Living soil system / Mineral weathering and parent material / Clay mineral transformation sequence

Clay mineral transformation sequence

The stepwise transformation of clay minerals, for example mica to vermiculite to smectite to kaolinite, as weathering removes potassium and silica.

Boundary: where this process starts

Starts with: Mica and feldspar lose interlayer K and alter to illite

Boundary: where it ends

Ends after: Clay mineralogy sets CEC, swelling and aggregate behaviour

PARTICIPANTSRESOURCESSoil solutionClay mineralsMicaIlliteVermiculiteOtherparticipantsClay mineralsPotassiumSilicaMagnesiumPrimarymineralsImpact +3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.35% base-rich, poorly draineImpact +4 of 5. Click for details and evidence.45% humid, well drainedImpact +4 of 5. Click for details and evidence.20% extreme leaching, tropicImpact +2 of 5. Click for details and evidence.Impact -2 of 5. Click for details and evidence.↻ balances · weak · 0.2Impact +3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact +3 of 5. Click for details and evidence.Impact +2 of 5. Click for details and evidence.↻ reinforces · weak · 0.15Impact +3 of 5. Click for details and evidence.Mica and feldspar lose interlayer K and alter to illite: makes Clay mineralsmakesMica and feldspar lose interlayer K and alter to illite: makes PotassiummakesMica and feldspar lose interlayer K and alter to illite: uses up Primary mineralsuses upInterlayer K loss opens layers; high-charge vermiculite forms: makes Clay mineralsmakesInterlayer K loss opens layers; high-charge vermiculite forms: makes PotassiummakesInterlayer K loss opens layers; high-charge vermiculite forms: uses MagnesiumLeaching intensity and silica activity decide the clay type: uses SilicaSmectite forms: 2:1 clay, high CEC and strong shrink-swell: makes Clay mineralsmakesSmectite forms: 2:1 clay, high CEC and strong shrink-swell: uses up Silicauses upSmectite forms: 2:1 clay, high CEC and strong shrink-swell: uses MagnesiumKaolinite forms with desilication: 1:1 clay, low CEC, little swelling: makes Clay mineralsmakesKaolinite forms with desilication: 1:1 clay, low CEC, little swelling: makes SilicamakesFixed K is re-fixed or slowly released from collapsed interlayers: uses PotassiumClay mineralogy sets CEC, swelling and aggregate behaviour: uses Clay mineralsformed as illiteClay minerals: formed as illitereleased frominterlayersPotassium: released from interlayersweathered into illitePrimary minerals: weathered into illitetransformed intovermiculiteClay minerals: transformed into vermiculitereleased as layers openPotassium: released as layers openfills interlayer sitesMagnesium: fills interlayer sitesactivity drives claytypeSilica: activity drives clay typeformed as smectiteClay minerals: formed as smectiteconsumed in smectiteformationSilica: consumed in smectite formationincorporated intosmectiteMagnesium: incorporated into smectiteformed as kaoliniteClay minerals: formed as kaolinitereleased duringdesilicationSilica: released during desilicationre-fixed or slowlyreleasedPotassium: re-fixed or slowly releasedcontrol CEC and swellingClay minerals: control CEC and swellingStart: Clay mineraltransformation sequenceSTARTStart: Clay mineral transformation sequenceEnd: Clay mineraltransformation sequenceENDEnd: Clay mineral transformation sequenceMica and feldspar loseinterlayer K and alterto illite📄1Mica and feldspar lose interlayer K and alter to illiteInterlayer K loss openslayers; high-chargevermiculite forms📄1Interlayer K loss opens layers; high-charge vermiculite formsLeaching intensity andsilica activity decidethe clay type📄1Leaching intensity and silica activity decide the clay typeSmectite forms: 2:1clay, high CEC andstrong shrink-swell📄1 ↗1Smectite forms: 2:1 clay, high CEC and strong shrink-swellKaolinite forms withdesilication: 1:1 clay,low CEC, litt…📄1Kaolinite forms with desilication: 1:1 clay, low CEC, little swellingGibbsite, goethite andhematite accumulate inextreme weathering📄1Gibbsite, goethite and hematite accumulate in extreme weatheringFixed K is re-fixed orslowly released fromcollapsed interlayers📄1Fixed K is re-fixed or slowly released from collapsed interlayersClay mineralogy setsCEC, swelling andaggregate behaviour📄1Clay mineralogy sets CEC, swelling and aggregate behaviour
Line thickness = size of impact (1 to 5)% on a line = chance a fork takes that branch📄 = pieces of evidence on a stepNegative effectLoops backHypothesisResource used up (arrow into the step)Resource used, not used upResource made or released (arrow out of the step)
What am I looking at? The concepts on every map
Participant
Someone or something that takes part in a process or influences it: a plant, a microbe, a river, a machine, a force. Participants are the rows of a map.
Resource
Something a step uses or uses up: water, oxygen, sunlight, a tool. Each step has an arrow down to the resources it uses.
Step
One thing that happens in a process. Every step has at least one participant and carries evidence.
Decision fork
A step where the process can go several ways. Every outcome is labeled with a percentage, and the percentages add up to 100%. It is not limited to yes or no.
Loop
A line that carries the process back to an earlier step. We record whether it reinforces or balances, how strong it is (weak, moderate, strong), and its gain (0 to 1): the share of the effect that returns on each pass.
Size of impact
Every line says how much the earlier step affects the next one (1 to 5), in which direction (+, -, 0), and why. Thicker lines mean bigger impact.
Evidence
The support for a claim: a source and what it shows. Every step, line, change and vote needs it. Click any step or line to read its evidence.
Boundary
Where a process starts and where it ends. Every process, and every subprocess, has a start and an end.
Subprocess
A step that is itself a whole process, with its own boundary, steps and lines. Click a step marked ↘ to open it. Subprocesses nest as deep as the evidence goes.
Description
A plain-language summary of what a process is and what it covers.
Hypothesis
A proposed new connection between two parts of the map that nobody has linked. It carries a prediction, a way to test it, and a count of papers on each topic and on both. It is an unverified idea until someone tests it.

Every step, with its evidence

The same information as the map, as a list you can search and share. Click a participant or resource to see everywhere it appears.

Mica and feldspar lose interlayer K and alter to illite
MicaIllitePotassiumPrimary mineralsClay minerals
Evidence (1) · added by Fern
  • Fanning & Keramidas 1977, Micas, in Minerals in Soil Environments (SSSA): Biotite and muscovite lose interlayer K+ to solution, leaving hydrous mica (illite) and expandable layers. (confidence 0.7)
Interlayer K loss opens layers; high-charge vermiculite forms
VermiculiteSoil solutionPotassiumMagnesiumClay minerals
Evidence (1) · added by Fern
  • Brady & Weil 2008, The Nature and Properties of Soils 14th ed., ch. 8 (silicate clays): Vermiculite is a weathered mica with high charge (CEC about 100-150 cmol/kg) and partly fixed interlayer K. (confidence 0.6)
⑂ Leaching intensity and silica activity decide the clay type
Soil solutionDrainage waterSilicaWaterBase cations
Evidence (1) · added by Fern
  • Borchardt 1989, Smectites, in Minerals in Soil Environments 2nd ed. (SSSA): Smectite favours Si- and Mg-rich solutions in poorly drained settings; strong leaching removes Si and favours kaolinite. Shares of outcomes are estimates (range 30-50%). (confidence 0.45)
Smectite forms: 2:1 clay, high CEC and strong shrink-swell
SmectiteClay mineralsMagnesiumSilica
Evidence (1) · added by Fern
  • Brady & Weil 2008, ch. 8: Smectites have CEC of roughly 80-150 cmol/kg and swell strongly on wetting. (confidence 0.7)
Kaolinite forms with desilication: 1:1 clay, low CEC, little swelling
KaoliniteClay mineralsSilica
Evidence (1) · added by Fern
  • Brady & Weil 2008, ch. 8: Kaolinite has CEC of about 3-15 cmol/kg and is non-expanding; dominant in strongly weathered humid soils. (confidence 0.7)
Gibbsite, goethite and hematite accumulate in extreme weathering
Iron oxidesAluminum oxidesIron oxidesAluminum
Evidence (1) · added by Fern
  • Sanchez 1976, Properties and Management of Soils in the Tropics (Wiley), ch. 3: Oxisols are dominated by kaolinite plus Fe and Al oxides with variable charge and anion sorption. (confidence 0.65)
Fixed K is re-fixed or slowly released from collapsed interlayers
IllitePlant rootsPotassium
Evidence (1) · added by Fern
  • Sparks & Huang 1985, Role of K in soils: potassium fixation, in Potassium in Agriculture (ASA): High K or drying collapses vermiculite layers (K fixation); depletion of solution K slowly releases it. (confidence 0.55)
Clay mineralogy sets CEC, swelling and aggregate behaviour
Clay mineralsSoilClay minerals
Evidence (1) · added by Fern
  • Brady & Weil 2008, ch. 8: Clay type controls CEC, shrink-swell and nutrient retention of the soil. (confidence 0.7)