CH.3 Geoscience Basics: Understanding Minerals and Crystallography

GEOL 215

What is ionic substitution in minerals?

The replacement of one ion by another in a mineral's crystal structure when ions have similar sizes and charges.

What is simple substitution?

Complete replacement of one ion by another in any proportion, creating a solid solution series.

What are end members in a solid solution series?

The pure forms of a mineral with only one type of ion in a specific site.

What is coupled substitution?

Simultaneous substitution of ions with different charges in different sites to maintain electrical neutrality.

What are miscibility gaps?

Ranges of compositions within a solid solution series that do not occur naturally due to limited substitution.

What does the phase rule state?

The number of phases (P) equals the number of components (C) plus two minus the degrees of freedom (F): P = C + 2 - F.

What is a liquidus in phase diagrams?

The temperature above which a substance is entirely liquid.

What is a solidus in phase diagrams?

The temperature below which a substance is entirely solid.

What occurs at a eutectic point?

A liquid cools to form two solid phases simultaneously.

What happens at a peritectic point?

A solid phase reacts with a liquid to form a new solid phase.

What are isotopes?

Atoms of the same element with different numbers of neutrons, leading to different atomic masses.

What is half-life in radioactive decay?

The time it takes for half of the atoms in a radioactive sample to decay.

What method uses the decay of uranium to lead for dating?

Uranium-Lead dating.

What type of dating uses rubidium decaying to strontium?

Rubidium-Strontium dating.

What is crystallography?

The study of the structure and symmetry of crystals.

How many crystal systems are there?

There are seven crystal systems.

What are Miller indices?

A system of three integers used to identify sets of parallel planes in a crystal lattice.

What does twinning in crystallography involve?

The intergrowth of two or more crystals of the same mineral with a symmetrical relationship.

What is the lever rule?

A method used to determine the relative proportions of phases in a two-phase region of a phase diagram.

What distinguishes crystalline substances from amorphous substances?

Crystalline substances have a highly ordered, repeating three-dimensional pattern.

What are the four types of symmetry operations?

Translation, rotation, reflection, and inversion.

What do space lattices represent?

Three-dimensional arrays of nodes or motifs where every node has an identical environment.

What defines a space point group?

It describes the rotational and reflection symmetry of three-dimensional motifs.

What are point defects in crystals?

Zero-dimensional defects involving individual atoms.

What is polymorphism?

The ability of a chemical compound to crystallize in more than one crystal structure.

What are reconstructive transformations?

Polymorphic transformations that involve breaking and reforming chemical bonds.

What are displacive transformations?

Transformations involving small shifts in atomic positions without bond breaking.

What are pseudomorphs?

Minerals that have inherited the external form of a pre-existing mineral, but have a different chemical composition.

What does hardness depend on in minerals?

Bond strength and bond density.

What is cleavage in minerals?

The tendency of a mineral to break along planes of weakness.

What does specific gravity measure?

The ratio of a mineral's density to the density of water.

What characterizes metallic luster?

Strong reflection of light typical of opaque minerals.

What is the difference between idiochromatic and allochromatic minerals?

Idiochromatic minerals have consistent color, while allochromatic minerals have variable color due to impurities.