Lecture 2
MINERALS LECTURE Sept. 5, 1996
1- Business
2- Scale in Geology (Time and Space; temporal and spatial)
3- Virtual Field trip
4- Why are rocks and minerals important?
5- Minerals
1- Introduction to the web page, homework, discussions.
2- Scale in Geology Geology deals with many different scales ranging from the ultramicroscopic to the universe dimensions.
Commonly we work from our own egocentric scale and work in either direction.
Next week Chuck DeMets will take us UPWARD into earth scale dimensions, today we will go DOWNWARD in scale our own scale to microscopic and sub-microscopic dimensions(Minerals)
We will go from "minds eye" size to dimensions both smaller and larger than can be comprehended without aid of other tools. (Telescope, microscope, large radio antennae, nuclear accelerators, ....)
A Virtual Field Trip
Good example will be to take a virtual walk to a geologic locality, collect specimens of rock from the locality, and examine these specimens closely.
Use a granite (IGNEOUS) and sandstone (SEDIMENTARY) as examples.
First note that the rock is "speckled" with different grains that are locked together in different ways, and that look different from one another.
Note that there are anywhere from one to four different types of grains.
Break granite or sandstone down to smaller sizes to DISAGGREGATE into its constituent particles.
Sort the grains into the different types (based on differing PROPERTIES, such as color, density, hardness, chemical composition).
Take any grain and further pulverize it and nothing new is produced, only smaller and smaller sized particles. Nonetheless we can still distinguish the different piles of separated grains from one another, but not within the piles.
We have reduced a rock to its fundamental building block a MINERAL.
Further note that at least one pile of minerals from each rock (sandstone and granite) is common to both rocks (QUARTZ and possibly FELDSPAR). Thus, different rocks may contain the same minerals, but in different proportions, and in the way the mineral grains are locked together. We'll discuss these features next week in our discussion of rocks.
3- WHY IS IT IMPORTANT TO KNOW ROCKS AND MINERALS?
Minerals form important natural materials used in the modern (and not so modern) world.
Examples include
Rock Physical Properties
The aggregate properties of minerals in rocks determine the behavior of these rocks in response to physical stress, such as in: Landslides Earthquakes Stream erosion Weathering and soil development
The strength, chemical stability, and response of rocks and minerals are all important factors in many, if not most, problems of environmental geologic nature.
Minerals and their recovery relate directly to world economies, political alliances, and potential environmental effects.
4- Minerals
Naturally ocurring materials that posess distinct physical and chemical properties that are either fixed or vary over a small range. Mineral species number in the thousands, yet only a handful constitute the vast majority of all minerals on the earth. Knowledge of as few as 30 common minerals is sufficient for most rocks on the earth. We distinguish minerals by their Properties, taken together allow distinction of unique mineral species. They are either fixed in their properties (as in minerals such as quartz and calcite) or vary within relatively narrow limits.
Typical diagnostic properties include:
WHAT DETERMINES THESE CHARACTERISTICS OF MINERALS?
Two Main factors
1- Their internal arrangement of atoms (crystal structure)
2- The ABUNDANCE of elements on the earth The abundance of elements relates to atomic reactions that occurred in the life and death of stars that preceeded our own sun's formation some 4.5 billion years ago.
A CRITICAL EXPERIMENT
Early investigations in the use of X-rays involved shining x-rays through crystalline substances. Place a sheet of film behind a crystal through which a narrow (collimated) beam of electrons are passed. Resultant RpictureS shows that the beam is diffracted into beams of differing intensity and angle from the direct beam. This DIFFRACTION of x-rays demonstrated that the atoms that make up crystals (minerals) have ORDERED INTERNAL ARRANGEMENTS of atoms.
MINERAL STRUCTURE
The ordered internal arrangement of atoms is distinctly different for different mineral species and allow us to determine the CRYSTAL STRUCTURE of the mineral. Represents an electrically balanced mix of negative (ex. O2-) and positive (ex. Si4+) atoms.
MINERAL COMPOSITION
Minerals may be comprisedof pure RnativeS elements:
Minerals may be chemically simple compounds:
Chemically complex
The most abundant mineral class Makes up > 99% of all earthUs crustal minerals Virtually ALL rocks are made up of various proportions of silicate minerals. Example structures:
NEXT WEEK Look at lithified mixtures of minerals (ROCKS) Discuss the characteristics, origin, and distribution of rocks on the planet Consider environmental aspects of rocks and their differences Strength Resistance to directed stress Resistance to chemical attack