<p>Kaolinite "grains", for want of any better term, are swollen with chemically bonded water compared to the crystals they weather out of so porosity is decreased by particle expansion while at the same time overall density drops. Kaolin also has very strong particle-particle adhesion so any mechanical deformation of the material tends to compress it leading to further reductions in bulk porosity. The influence of Calcium and Potassium on the ongoing weathering of the rock and it's overall porosity depends greatly on the weathering regime; for example if weathering is continuously under wet conditions then Calcium and Potassium will be mobilised in ground water and removed. On the other hand in a wetting-drying cycle Calcium and Potassium liberated from the parent rock become oxides when the material dries out, those subsequently react strongly with water in the next wetting cycle acidifying the environment and accelerating rock decomposition.</p>

CC BY-SA 4.0
2018-06-07T11:21:05.070Z
Another part of my research plans on linking ion presence in an adjacent lake to the weathering of this granodiorite since the area I am studying is fairly humid year round. I believe groundwater would eventually trickle into the river hence carrying these ions with them. I assume it's also possible for ions to get "stuck" in the rigid confines of the mineral and react with excess water to form more oxides augmenting decomposition that way?
Yaboy33
CC BY-SA 4.0
2018-06-10T15:27:08.213Z
@Yaboy33 Usually in wet environments it's Hydroxides that form rather than Oxides, drying is usually a key step in forming Oxides rather than Hydroxides.
Ash
CC BY-SA 4.0
2018-06-06T17:42:25.330Z
2018-06-06T17:55:39.887Z
2018-06-06T17:55:39.887Z
Ash
<p>I started studying the effects of weathering on granodiorite (see previous posts) and plan on referencing the link between the chemical weathering of feldspar plagioclase leading to kaolinization, a process I am relatively unfamiliar with. In brief terms, how would this reaction reduce the porosity of the rock? Also, how would the release of $Ca$ and $K$ influence further degradation of the rocks porosity? </p>

CC BY-SA 4.0
2018-06-06T09:37:20.370Z
They are slightly weathered. So it seems the production of kaolinite increases porosity?
Yaboy33
CC BY-SA 4.0
2018-06-06T09:44:19.817Z
@Universal_learner What about the transition of granodiorite to a saprolite form. These are apparently more-porous and clay-based (kaolinite). Am I missing something?
Yaboy33
CC BY-SA 4.0
2018-06-06T10:11:25.397Z
@Universal_learner What's the distinction between "effective" and "full" porosity?
Yaboy33
<geology>
How does the synthesis of Kaolinite (and it's by products) influence porosity in granodiorite?
Yaboy33
# How does the synthesis of Kaolinite (and it's by products) influence porosity in granodiorite?

(Asked by: username_0 on 2018-06-06)

I started studying the effects of weathering on granodiorite (see previous posts) and plan on referencing the link between the chemical weathering of feldspar plagioclase leading to kaolinization, a process I am relatively unfamiliar with. In brief terms, how would this reaction reduce the porosity of the rock? Also, how would the release of $Ca$ and $K$ influence further degradation of the rocks porosity?

**Tags:** geology

> **Comments:**
> **username_0**: They are slightly weathered. So it seems the production of kaolinite increases porosity?  
> **username_0**: @Universal_learner What about the transition of granodiorite to a saprolite form. These are apparently more-porous and clay-based (kaolinite). Am I missing something?  
> **username_0**: @Universal_learner What's the distinction between "effective" and "full" porosity?  

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## 1 answers

### Answer by username_1 on 2018-06-06. Score: 2 | Accepted answer

Kaolinite "grains", for want of any better term, are swollen with chemically bonded water compared to the crystals they weather out of so porosity is decreased by particle expansion while at the same time overall density drops. Kaolin also has very strong particle-particle adhesion so any mechanical deformation of the material tends to compress it leading to further reductions in bulk porosity. The influence of Calcium and Potassium on the ongoing weathering of the rock and it's overall porosity depends greatly on the weathering regime; for example if weathering is continuously under wet conditions then Calcium and Potassium will be mobilised in ground water and removed. On the other hand in a wetting-drying cycle Calcium and Potassium liberated from the parent rock become oxides when the material dries out, those subsequently react strongly with water in the next wetting cycle acidifying the environment and accelerating rock decomposition.

> **Comments:**
> **username_0**: Another part of my research plans on linking ion presence in an adjacent lake to the weathering of this granodiorite since the area I am studying is fairly humid year round. I believe groundwater would eventually trickle into the river hence carrying these ions with them. I assume it's also possible for ions to get "stuck" in the rigid confines of the mineral and react with excess water to form more oxides augmenting decomposition that way?  
> **username_1**: @username_0 Usually in wet environments it's Hydroxides that form rather than Oxides, drying is usually a key step in forming Oxides rather than Hydroxides.  

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