CH.2 Geoscience Basics: Understanding Minerals and Crystallography

What is ionic substitution in mineral formation?

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, exemplified by olivine.

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 express?

The relationship P = C + 2 - F, where P is the number of phases, C is the number of components, and F is the degrees of freedom.

What is the liquidus temperature?

The temperature above which a substance is entirely liquid.

What is a eutectic point on a phase diagram?

A point where a liquid cools to form two solid phases simultaneously.

What is radioactive decay?

The spontaneous transformation of an unstable isotope into a more stable isotope.

What is half-life in terms of radioactive isotopes?

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

How does Uranium-Lead dating work?

It uses the decay of uranium isotopes to lead isotopes to determine the age of a rock.

What are isotopes?

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

What are Miller indices?

A system of three numbers used to identify crystallographic planes.

What is the smallest repeating unit of a crystal lattice called?

Unit cell.

What is the role of twinning in crystallography?

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

How many crystal systems are there?

There are seven crystal systems.

What is the lever rule used for?

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

What is the definition of solidus temperature?

The temperature below which a substance is entirely solid.

What is a discontinuous reaction series?

A series of minerals that change abruptly during crystallization or melting.

What is silica saturation?

The relative abundance of silica (SiO₂) in a system, influencing mineral formation.

What is the significance of isotopic ratios in geology?

They are used in various geological applications, such as dating and tracking geochemical processes.