Minerals Flashcards
What are minerals?
Inorganic, naturally occurring solids. They are crystalline substances with characteristic internal structure, and chemical compositions that are either fixed, or vary within fixed limits.
What are some organic materials?
Vegetation, coal, oil, and gas are all derived from strictly organic sources. Therefore, none of these are minerals.
Many organisms do what that allow them to count as minerals?
They secrete/metabolize shells and hard parts that are identical to true minerals that can also be produced by inorganic processes.
Inorganic does NOT mean…
has no carbon (e.g. diamonds and graphite) even though earth has carbon-based life forms.
Are synthetic compounds minerals even if they conform to the definition?
No, even if synthetic compounds conform to the definition in every way, they don’t count because they are not naturally occurring.
Can liquids or gases be minerals?
No, minerals must be solids at atmospheric temperature and pressure. However, water in the form of ice does count as a mineral.
What does having a crystalline structure imply?
That the mineral has a consistent, repeating, internal arrangement of atoms.
Why isn’t glass a mineral?
Because glass has no ordered arrangement of atoms and is therefore amorphous (lacking a clear structure).
A-(without)-morphous-(shape).
How are minerals fixed or vary within fixed limits?
Some minerals have fixed chemical compositions (quartz, SiO2, and calcite, CaCO3) whereas others vary due to ionic substitution (plagioclase feldspar and olivine).
Minerals are nothing more than _______ that conform to their definition
chemical compounds
What things are bonded to make stable chemical compounds?
Atoms, ions, ion groups and molecules.
What are some interparticle bond types?
Ionic bonds, covalent bonds, and van der Waal’s or residual bonds
How is a cation formed?
When atoms of an element give up one of more electrons to become positively charged.
How is an anion formed?
When electrons are accepted by an element to become negatively charged.
How is an ionic bond formed?
When cations and anions are connected by a strong electrochemical bond; both the cation and anion achieve a stable elcetron configuration. E.g. NaCl
A greater variety of minerals use _____ bonds more than any other type.
Ionic
How are covalent bonds formed?
When electrons are shared between atoms (may be of the same or different element) to achieve a stable electron configuration.
How are the bonds in a diamond different from the bonds in graphite?
In a diamond, each C is single-bonded to 4 other C atoms whereas in graphite, at a different pressure and temperature, each C is bonded to 3 other C atoms in alternating single and double bonds (like a benzene ring) to produce sheets bonded to each other with van der Waal’s bonds.
How are van der Waal’s/ residual bonds formed?
Electrical asymmetry of bonded atoms and molecules produce weak residual surface charges; these are weak bonds that are easily broken, think of graphite on paper.
What is the name for different minerals, such as diamonds and graphite that have the same chemical composition but different crystalline structures?
Polymorphs.
Poly-(many)-morphs-(forms).
Minerals are crystalline by virtue of what characteristic?
Their ordered internal arrangement of atoms, not by their external form.
What causes imperfections on minerals?
Mutual interference, flaws caused by growth irregularities (think of tetris), and impurities.
What is a unit cell?
The minimum repeating structural entity within the structure; usually on the order of a few to less than 20 A
Why are crystals variable in shape?
Because the crystal grows by addition of unit cells to the lattice at variable rates in different directions, therefore, crystals aren’t just exact copies of each other.
The regular structure and electron configuration of crystals give chemical stability and may allow…
atoms of two elements of similar size and charge to substitute for each other in the structure/lattice (they both “fit”).
An example of a mineral with a variable within fixed limits is…
Also, what is the term for this type of variable within fixed limits?
Olivine which may have either magnesium, iron, or any mixture of the two as its cation in its chemical composition. This is called solid solution (a range of compositions).
What allows us to identify minerals?
The combination of chemical compositions and crystal structures which is characteristic of each mineral.
How is hardness of minerals measured?
Using Mohs Hardness Scale (know). It is only a relative scale, it’s not linear or logarithmic.
What is cleavage?
Cleavage exists if there are directions or planes of weakness in the crystal structure of a mineral. A single cleavage repeats several times in a single crystal. Many minerals have 2 or more cleavages (feldspar, calcite) whereas some minerals have none (quartz).
