12 - Lecture notes for Clay Mineralogy


Required reading: Moore and Reynolds, 117-125, 155-168
Brindley and Brown, pages 305-360


XRD identification of discrete clay minerals


Vermiculite
- Operationally defined as those layers that expand to 14.5 after Mg-saturation and solvation with glycerol (not ethylene glycol - both polar organic compounds). Smectites will expand to 18. If ethylene glycol is used, then smectite expands to about 17.

Vermiculite accepts one layer of glycerol and smectites accept two layers of glycerol.

(1) Mg-vermiculite

Distinguishing vermiculite from smectite is not always foolproof. In reality, both mineral groups exhibit a range of layer charges. Those vermcilulites with higher layer charge (e.g., 0.8) will readily collapse, while those with lower layer charge (e.g., 0.6) will readily expand.

Also, the presence of hydroxy-interlayers (HIV) will prop the structures open and the XRD characteristics begin to resemble those of chlorite.

Vermiculites and smectites are best diagnosed by performing a number of different cation saturations, solvations and heatings. See page 12 of handout. Mg, Ca vs. Na vs. K saturations.

(2,3) Mg-vermiculite vs. Fe-vermiculite Ratio of the (003)/(002)


Smectites - Operationally defined as those layers that expand to 17 upon ethylene glycol solvation.


(4, 5, 6, 7) Interlayer water.

 
Why does talc (with no layer charge) have no interlayer water?



Mixtures of discrete clay minerals

Most often in nature we encounter mixtures of minerals (i.e., a mineral assemblage).  How do we discriminate mixtures.

For example we can have a range of hydration states within a smectite alone.  The extreme (and not realistic) example is a 50/50 mixture of hydrated and dehydrated smectite.




Another example (maybe more realistic is a 50/50 mixture of 1-water and 2-water hydration states.



What would happen if the 1-water and 2-water layers were randomly stacked? This brings to our attention the concept of a mixed-layer clay mineral.  Below is an example of a 50/50 randomly mixed layer mineral.


What would happen if the 1-water and 2-water layers were stacked in an ordered fashion? This again brings to our attention the concept of a mixed-layer clay mineral.  Below is an example of a 50/50 ordered mixed layer mineral.




Click here for a table that shows changes in low angle reflection (00l) of discrete clay minerals with ethylene glycol and thermal treatments.



Palygorskite and Sepiolite structures.

 
-