Introduction to minerology Flashcards
Define and explain what a mineral is:
A mineral is a naturally occurring solid with a highly ordered atomic arrangement and a definite (but not fixed) chemical composition. It is usually formed by inorganic processes.
Describe the abundances of elements and minerals on Earth:
- Oxygen (O) and Silicon (Si) are the most abundant elements in the Earth’s crust.
- Iron (Fe) and Magnesium (Mg) are relatively high in abundance due to their presence in minerals such as olivine and pyroxene.
Identify and label common cations and anions in mineral formulae and illustrate their size:
- Common cations include Na+, Mg2+, Al3+, Si4+, K+, Ca2+, Fe2+ and Fe3+.
- Common anions include CO3^2-, PO4^3-, Cl-, F-, O2-, SiO4^4-, SO4^2-, S^2-, and OH-.
- The size of cations and anions can vary, and their relative sizes determine how they “fit” together in a mineral structure.
Use cation/anion substitutions and binary and ternary plots to explain solid solutions and miscibility:
- Cation substitutions occur when cations of similar charge and size replace each other within the same crystal structure.
- Binary solid solutions involve two end-members, where cations substitute for each other.
- Ternary solid solutions comprise three end-members with solid solution between them.
- Miscibility gaps can occur when minerals are only stable over a certain chemical composition range.
Define crystalline:
Crystalline refers to any solid compound with an ordered, repetitive atomic structure. All minerals are crystalline by definition.
Describe the types of conditions under which minerals form:
- Minerals form through the bringing together and ordering of constituent elements in a fluid.
- Factors influencing mineral formation include temperature, time, abundance of elements/atoms, and the presence or absence of a fluid (flux).
Define what a mineral group and mineral class are and explain how minerals are classified:
- A mineral group consists of two or more minerals with similar crystal structure and the same anionic group.
- A mineral class comprises minerals with the same anion or anionic complex but varying crystal structures.
- Minerals are classified based on their crystal structure, chemistry, and anionic composition.
Describe how cations and anions are organized in mineral formulae:
- Mineral formulae list cations first, followed by anions, to ensure charge balance.
- Cations occupying the same site are grouped together, and cations in different sites are listed in decreasing order.
Define the unit cell and use translation to create crystal structures:
The unit cell is the smallest, unique, repeat volume in a crystal structure.
Crystal structures are created by repeating and translating unit cells in three dimensions.
Use the lengths and angles of the reference axes to draw and define the six crystal systems:
The six crystal systems are:
isometric/cubic (a1=a2=a3)
tetragonal - (a1=a2≠c)
orthorhombic - (a≠b≠c)
hexagonal - (a1=a2=a3) + 1 long C axis
monoclinic - (a≠b≠c) - 2 angles 90°, one is not
triclinic - (a≠b≠c) - all angles ≠90°
Distinguish certain minerals using ONLY crystal systems:
Isometric/Cubic System: pyrite, galena, and halite.
Tetragonal System: zircon, cassiterite, and rutile.
Orthorhombic System: topaz, aragonite, and orthoclase.
Hexagonal System: quartz, calcite, and beryl.
Monoclinic System: gypsum, orthopyroxene, and clinopyroxene.
Triclinic System: plagioclase feldspar, microcline, and labradorite.
List and illustrate several crystal habits:
Crystal habits refer to the shape or form that crystals exhibit during growth.
Common crystal habits include euhedral (well-formed), anhedral (irregular), prismatic (elongated), acicular (needle-like), and massive (lacking distinct shape).
