Clay minerals determine shrink/swell soils

Geology and Climate Control the Formation of Clay Minerals

Granite is made up of quartz, mica and feldspar. As quartz is resistant to chemical weathering, it may be eroded only as mineral grains of quartz. Feldspars and micas are susceptible to chemical weathering and break down to form clay minerals.

The main group of clay minerals are kaolinite, illite and montmorillonite. The layers in kaolinite are held together by fairly weak bonds, whereas there is strong bonding in illite and montmorillonite because of the presence of positively charged metal ions; potassium in the case of illite, and calcium and sodium in the case of montmorillonite.

Generally, potassium feldspar breaks down to form kaolinite; micas weather to give illite, and ferromagnesian minerals break down to form montmorillonite.  This chart shows that precipitation is also an important factor:

Source (PDF): Clay mineral formation and transformation in rocks and soils.  Eberl.  Phil. Trans. R. Soc. London 1984 

Alternating dry and wet climates can be inferred by the types of clays formed:



The major types of clay
Kaolinite, smectite (montmorillonite) and Illite:



1:1 Kaolinite
The sum of the many hydrogen bonds between micelles results in the micelles being very strongly bonded together and nearly impossible to separate. This bonding of the layers together results in kaolinite being a nonexpanding clay mineral. Since each micelle is constructed of a layer of silicon tetrahedral units and a layer of octahedral units, kaolinite is called a 1:1 clay mineral.

Kaolinite is formed by weathering or hydrothermal alteration of aluminosilicate minerals. Thus, rocks rich in feldspar commonly weather to kaolinite.  In order to form, ions like Na, K, Ca, Mg, and Fe must first be leached away by the weathering or alteration process.  This leaching is favored by acidic conditions (low pH).  Granitic rocks, because they are rich in feldspar, are a common source for kaolinite.



2:1 Smectite (AKA Bentonite) and Vermiculite
Smectites have more Mg2+, Fe2+, or Mn2+ substituted for Al, giving their sheets a permanent negative layer charge, which in turn leads to high CEC values.  Montmorillonite is a type of smectite.  Montmorillinite is the main constituent of Bentonite, derived by weathering of volcanic ash.   Smectites have a high shrink/swell capacity because water molecules can intercalate between the clay sheets, greatly expanding their total volume.

2:1 Illites
Illite clays are non-expanding.  Illites are formed from weathering of K and Al-rich rocks under high pH conditions. Thus, they form by alteration of minerals like muscovite and feldspar. Illite clays are the main constituent of ancient mudrocks and shales.

2:1 Vermiculite
Vermiculite weathers from mica, which often forms at the contact between felsic and mafic rocks.  It swells intermediate amounts.

 Minerology maps of the U.S (PDF)
example:  calcium carbonate map:

 New Mexico shrink/swell clays:

Source:  Swelling clays map of the conterminous United States.  From a good website.

MAP LEGEND

Unit contains abundant clay having high swelling potential Part of unit (generally less than 50%) consists of clay having high swelling potential Unit contains abundant clay having slight to moderate swelling potential Part of unit (generally less than 50%) consists of clay having slight to moderate swelling potential Unit contains little or no swelling clay Data insufficient to indicate clay content of unit and/or swelling potential of clay (Shown in westermost states only)

Excess or Insufficient Micronutrients?

Some authors have argued that excess micronutrients, specifically zinc, iron, and copper are a cause of a number of diseases, from atherosclerosis to Alzheimer's. (1) But other writers argue that most Americans are micro nutrient-deficient (very few Americans are macronutrient deficient!). (2)

Micronutrients are critical for human health, but many have relatively narrow ranges associated with optimal health.  Assuming that U.S. dietary guidelines are valid (debatable, but a good starting point), how many people really are receiving inadequate or overabundant micronutrients?

I searched journal articles featuring contemporary data from the U.S. NHANES which surveys a representative sample of the U.S. population.  

Large portions of the population had total usual intakes (food and supplement use) below the estimated average requirement for vitamins A (35%), C (31%), D (74%), and E (67%) as well as calcium (39%) and magnesium (46%). Only 0%, 8%, and 33% of the population had total usual intakes of potassium, choline, and vitamin K above the adequate intake when food and multivitamin use was considered. The percentage of the population with total intakes greater than the tolerable upper intake level (UL) was very low for all nutrients; excess intakes of zinc were the highest (3.5%) across the population of all of the nutrients assessed in NHANES.(3)

Population-based studies indicate that vegetarians have lower mean intakes of vitamin B-12 and zinc and higher intakes of fiber, magnesium, and vitamins A, C, and E than do nonvegetarians. Usual intake data suggest a similar prevalence of inadequacy between vegetarians and nonvegetarians for magnesium and vitamins A, C, and E, with both groups at high risk of inadequate intakes of these nutrients. These same data report that vegetarians have a higher prevalence of inadequacy for iron, vitamin B-12, protein, and zinc than do nonvegetarians. Vegetarians should optimize intakes of vitamin B-12, zinc, and protein; and both vegetarians and nonvegetarians need to increase intakes of calcium, magnesium, fiber, and vitamins A, C, and E. (4)

But these studies only analyze reported food intake, which is notoriously unreliable, even, possibly, in NHANES. Interestingly, NHANES also does actual blood tests, and the results from that research found very few physiologyical (as opposed to dietary) deficiencies.  CDC's National Report on Nutritional Indicators (2012, valid for the period 2003-2006,  only found deficiencies in B6 (11%), Iron (women: 10%), Vitamin D (8%), Vitamin C (6%).   This same report indicates that folate supplementation is responsible for lowering deficiency to less than 1% of the U.S. population.  They also note that many women have iodine levels "bordering on insufficiency".  They did not note any micronutrient excesses. (5)

Sources:

(1) Power Foods for the Brain.  Barnard, Neil.  2013

(2) see, for example, http://chriskresser.com/are-supplements-really-necessary and http://chriskresser.com/why-you-should-think-twice-about-vegetarian-and-vegan-diets

(3) J Am Coll Nutr. 2014;33(2):94-102. doi: 10.1080/07315724.2013.846806.

Multivitamin/mineral supplement contribution to micronutrient intakes in the United States, 2007-2010.

Wallace TC1, McBurney M, Fulgoni VL 3rd. (Affiliation: Council for Responsible Nutrition)

(4) Am J Clin Nutr. 2014 May 28;100(Supplement 1):365S-368S.

Nutritional adequacy of plant-based diets for weight management: observations from the NHANES.

Farmer B.PlantWise Nutrition Consulting LLC

(5) Second National Report on Biochemical Indicators of DIet and Nutrition in the U.S. Population. 2012

Regolith -- Silicate Mineral Weathering

All diagrams are from the excellent :

Regolith Geology and Geomorphology
G. Taylor, R. A. Eggleton, Richard A.. Eggleton
John Wiley & Sons, Aug 30, 2001