Definition of mineral: naturally occuring, inorganic, fixed or limited range of chemical composition, crystalline (regular atomic arrangement of constituent ions).

Major groups of minerals:

• silicates: the most common type of mineral, relatively low solubility, quartz and feldspars the most common terrestrial minerals, feldspars weather to clays.
• clays: these are mostly silicates, but very fine-grained, with a sheet geometry and some with distinctive shrink-swell propertites.
• oxides: typically consists of a metal linked to oxygen, solubility is sensitive to conditions.
• sulfides: typically consists of a metal linked to sulfur, solubility is sensitive to conditions, unstable in oxygenated surface environments producing acidity as a product.
• salts (evaporites): soluble, and important to biologic activity.
• carbonates: has a carbonate radical (carbon linked to three oxygens), relatively soluble, produces hard water.
• we will introduce minerals in specific contexts as lecture goes along.

Sediment versus hard rock, a basic distinction.

How can sediment be described?

• color(s).
• size distribution of particles.
• shapes of particles.
• mineral make-up of particles.
• alignment and geometry of particles (e.g. packing).
• average chemical composition.
• organic content.
• for each of this you can think on how it might be described/measured, and how that information might be useful.

Description on the basis of grains size: mud -> silt -> sand (fine to medium to coarse) -> gravel -> boulders.

If you think of surface sediment the particles come in different sizes. How would knowing the size distribution of surface sediment be of potential interest environmentally?

Lithification = process whereby sediment -> rock, sand -> sandstone.

How can rocks be described and classified?

• color, density, mineral make-up, isotropic vs. anisotropic, chemical composition.
• different classifications for different purposes.
• three fold basic genetic classification:
  • igneous
  • sedimentary
  • metamorphic
  • + hydrothermal.

From an environmental perspective what are important rock and/or sediment properties? What would you want to know more specifically about a given rock or sediment type from an environmental perspective? Why is this information useful.

• strength (e.g. compactability or elasticity).
• density.
• specific chemical consitutents such as;
  • heavy metals such as lead (Pb), mercury (Hg).
  • sulfides and/or oxides.
• radioactivity.
• solubility.
• seismic properties.

What near surface processes alter geologic materials?

• physical breakdown.
• chemical alteration (silicates to clays, production of oxides).
• solution.
• cementation and precipitation.
• bioturbation, bioerosion.

• earthquakes.
• volcanic eruptions.
• mass wasting.
• soil erosion.
• coastal erosion.
• flooding.
• subsidence, collapse.
• radon, asbestos, other geologic toxins.
• meteorite impacts.
• we will, once again learn more about each of these and other concerns in specific contexts as the course goes along.

Earth processes important in understanding geologic resources:

• hydrologic cycling, including groundwater flow.
• geothermal processes (heat flow, hydrothermal systems).
• soil forming processes.
• fossil fuel forming processes.
• ore forming processes.

We will focus a bit more on groundwater flow for several reasons:

• it is becoming a more and more important resource.
• much environmental industry is related to the cleanup and management of groundwater.
• since it is hidden from sight, most are less familiar with it.

How does the water get into the ground?

An answer may be found in considering part of the hydrologic cycle. The diagram below attempts to show some of the reservoirs linked to groundwater, and the processes that transfer water between these reservoirs.

This leads to a second question. What determines how much seeps into the ground?

• soil porosity/ permeability (what in turn determines this?).
• slope.
• rainfall or seepage flux (rate of supply of the water).
• captured in the concept of recharge rate. For a partly depleted groundwater reservoir how long will it take for water to refill it.

How much water can the ground hold (what is its porosity)?

• definition: percentage of void space within rock body under consideration.
• two types:
  • intergrain: space between grains, porosity typical of sediment.
  • fracture: space provided by fractures, typical of hard rock.
• what attributes of the fracture system control fracture porosity?
• determining factors on intergrain porosity -> sorting, packing, and grain shape.
• 
• The above diagrams illustrate in 2-D how sorting and packing effect porosity.
• how can porosity be measured?
• representative values for various geologic media: conglomerates and sandstones - 20-40%, muds - 60%, shales (lithified muds) up to 10%.

What determines in what pattern and how fast water flows in the ground?

• intergrain permeability: influencing factors -> porosity, geometry of pore spaces, grain size.
• fracture permeability: common in crystalline rocks, anistropy of permeability.

How can we map groundwater surfaces (given they are hidden from view)?

• surface manifestations and connections.
• monitoring vs. extraction wells.
• geophysical techniques.
• modeling.
• contoured surfaces and shallow flow nets.

Aquifer is a groundwater reservoir. What are local aquifers (for Omaha area)?

Dr. Schimmrich has collected links to hydrology and hydrogeology.