Chapter 2: Minerals
Geologists study minterals both to understand the formation of rocks and to locate and extract
resources that you use every day.
Many rocks look uniform from a distance, but upon closer examination clearly consists of
smaller components called minerals.
Luster – The property that describes how mineral surfaces reflect light.
Crystal Faces – Distinct faces that minerals have which are smooth, flat surfaces with regular geometric
Specific Gravity – The weight of a material in air divided by the weight of an equivalent volume of water
at 4 degrees celcius.
Hardness – A measure of the resistance of a mineral surface to scratching.
- Measured using the Mohs Hardness Scale. It is a relative scale with values b/w 1 - 10
Cleavage – Describes the flat, smooth planes along which some minerals break and the shape of the
- Non-uniform breakage is fracture, rather than cleavage.
Color is not always a reliable property for identifying a mineral because many minerals can have
the same color.
Color Streak – The color of the residue produced by scratching a mineral on a nonglazed porcelain plate.
- A mineral may vary in color, but its streak color is always the same.
What are the Properties of Minerals?
Minerals have observed or easily measured physical properties, some of which are more
diagnostic than others for recognizing a specific mineral.
The principal physical properties used to describe the minerals are color, luster, streak, hardness,
cleavage, specific gravity, and external crystal form.
What are Minerals Composed of?
Minerals are chemical compounds consisting of combinations of atoms of one or more elements.
Each mineral has a definitive, but possibly slight varying, chemical composition.
How do we know…the Atomic Structure of Minerals?
Geologists use TEM microscropes to visualize arrangements of atoms inside minerals. TEM images, made by firing electrons into a mineral sample, show the orderly internal
arrangement of atoms unique to each mineral.
Each mineral consists of atoms of particular elements arranged in an orderly pattern.
Distribution of electrons around atomic nuclei determines how atoms bond.
Ions – Positively or negatively charged particles.
Ionic Bonds – Formed by the attraction of negative & positive ions in order to balance their charges.
Covalent Bonds – Two or more atoms mutually share electrons to fill the outer electron layer.
Metallic Bonds – Electrons roam freely around a number of different atoms, typically of the same
element. This explains why metallic substances can conduct electricity.
Van der Waals Force – Weak attraction of neutrally charged particles.
Minerals solubility in water depends on the strength of the ionic bonds.
o Adding acid to water can further enhance solubility.
Polymorph – Minerals with identical chemical composition but with different arrangements of atoms.
How do Elements Combine to Make Minerals?
Minerals are atoms of elements combined by ionic, covalent, and less common metallic bonds
and weak van der waals forces.
Ionic bonds are weaker than covalent bonds, where atoms share electrons.
The neutral, but lopsided, water molecule has a weak positive charge at one end and a negative
charge at the other. These charges pull apart some weakly bonded ions, causing some minerals
to dissolve in water.