Felsic and Mafic Rock Types

 

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)

Regolith and Quarternary Sedimentology: questions to infer paleogeomorphology and paleoclimate

This image was taken along Las Huertas creek, near the village of Placitas.  Note the lack of developed soil horizons: the top layers appear to be unconsolidated colluvial debris.   Perhaps the sandstone layers below the Juniper roots are paleo-sand dunes?  What then might the different colors indicate?

This image and the following were taken along La Jencia creek, deeply incised into Pleistecene and Holocene sediments in the San Lorenzo Spring quandrangle west of Socorro, NM.    The layers exposed along the creek channel show darker clay and/or organic-enriched layers that may have formed from swamps and/or backwaters along paleochannels.

Screenshot of the Quandrangle geological map, with a red dot on La Jencia creek showing the location of the photos.

This exposure reveals an unconformity in the left-center that may be due to in-filling of a paleo channel?  Does this images show an actual unconformity, with deposition, then erosion, then deposition? Or was there continuous deposition? Why is there banding of light and dark material in such regular layers?  How were these layers laid down?  Does the fact that they were deposited indicate an aggrading landscape, perhaps controlled by climate-influenced sediment supply??

This photos shows a close-up of a tiny (5-foot long) layer of darker clay, clearly deposited in a concavity.  Note the coarser sediment deposited below it and the finer sediment above.  How old are these layers?  How do geologists infer the direction of paleoflow?  Why aren't there fossils?

Surface geology maps of the area offer confusing clues to interpreting these buried layers.  The geological map for the quandrangle to the North of San Lorenzo Springs (the Silver Creek quandrangle) shows paleochannel flows on the surface, as well as relictual dunes from some point in the Quarternary.  Why are the paleochannel flows going every which way?  Was this whole valley a closed basin, and if so, would that explain the aggradation, independent of sediment supply?  Why is this stream downcutting so rapidly today?  What are the implications for the future?

Maps to work site: Paliza, Jemez Mountains

Link to all NM Geologic Maps.
Link to all NM topographic maps.

Dendritic Stream Branching in the Piedmont and Triassic Basic

Who can spot Chapel Hill??

7 types of Igneous Rocks

Sunspots, Space Weather, and the Earth

Prikryl et al 2009: Solar magnetic sector boundary passage (SBP) and vorticity area index (VAI), by weather reconstruction ERA-40 dataset back to 1963-2002, confirmed the "Wilcox effect". The interplanetary magnetic field and associated "space weather" directly effect Earth's weather.

News from Dr. Leif Svalgaard at Stanford:

Wolf was right...we can use magnetic field strength to calibrate solar irradiance. The correlation between solar far-UV radiation and geomagnetic force on the Earth's surface is extremely good;

now we have an objective calibration for sunspot number.
The conclusion? Leif 2007 finds no long-term trend in solar irradience from at least 1600. through the present.

Geology of Carnero Canyon

The Map Room. This is where most of our adventures start.
View up Carnero Canyon toward Hell's Gate, beyond which lies our cabin.
There is pillow lava here, scattered about, but especially in the next canyon over.
Penitente Canyon and the view toward the San Luis Valley and Sangre de Cristo Mountains.
Awesome columnar jointing on the South side of the Hell's Gate
North Side.

Back side.

Soil Horizons and Taxonomies

"Soils tend to have distinct variations in color both horizontally and vertically. The coloring of soils occurs because of a variety of factors. Soils of the humid tropics are generally red or yellow because of the oxidation of iron or aluminum, respectively. In the temperate grasslands, large additions of humus cause soils to be black. The heavy leaching of iron causes coniferous forest soils to be gray. High water tables in soils cause the reduction of iron, and these soils tend to have greenish and gray-blue hues. Organic matter colors the soil black. The combination of iron oxides and organic content gives many soil types a brown color. Other coloring materials sometimes present include white calcium carbonate, black manganese oxides, and black carbon compounds."

NRCS's "12 Orders of Soil Taxonomy

What's Inside the World?

A century ago people didn't know what the interior of the Earth looked like...but they had many ideas, extrapolated from what they did know: thousands of miles of jungle caves?? Feel free to contribute your own rendition of what's inside. The psychological importance of the Earth and our conception of it can be read off mind-maps like these. They say more about what is inside each of us than what is outside. But what is inside the Earth?