303: Mineralogy Exam 1 [Vocab]

Prism

faces parallel to an axis

Pinacoid

a crystal form whose faces are parallel to two crystal axes.

Pyramid

non-parallel faces meet at a point with A3, A4, or A6

Scalenohedron

non-parallel faces meet at a point with A3 bar or A4 bar

Rhombohedron

all axes are of equal length. None of the axes is perpendicular to another. All crystal faces have the same size and shape.

Trapezohedron

non-parallel faces meet at a point with offset

Open Forms

one or more crystal faces that do not completely enclose space

Closed Forms

 set of crystal faces that completely enclose space

Enantiomorphic

indicates an inversion point (i)

2/m, 3/m, 6/m

a 2/3/6 fold axis with mirror symmetry

Polymorph

minerals with the same chemical composition may/can express different crystal structures depending on the temperature and pressure at which they formed

Isomorph

a mineral can have the same crystalline shape and general appearance despite a range of chemical compositions that result in the same mineral

Pseudomorph

mineral formed by chemical or structural change of another substance, but retains its external shape.

Solid-solution

two or more elements that can easily substitute for each other due to similar ionic size and charge.

Anion complex

a complex ion that is negatively charged

Twinning

symmetric intergrowth of two or more crystals of the same mineral

Polysynthetic twin

the composition surfaces are parallel to one another

Penetration twin

crystals that pass through one another and often share the center of their axial systems

{111} vs. (111)

{} indicates a group of phases and () is one phase

h, k, l

plane that intercepts three points a1(h), a2(k), a3(l). Represents a point on the plane identified by Miller indices

Inert gas

A gas that does not readily undergo chemical reactions with other chemical substances and therefore does not readily form chemical compounds

Moh’s Hardness

hardness scale to determine the hardness of a mineral

Euhedral

has all crystal faces

Mineraloid

a mineral that has 3 of the 4 criteria that make up a mineral usually excludes repeating internal structure

Crypto-crystalline

10x-1000x vision of crystal (max to get on microscope)

Micro-crystalline

<1000x vision can only be seen with SEM or x-ra

Anhedral

has no crystal faces

Ions

any atom or group of atoms that bears one or more positive or negative charges due to loss/addition of electrons

Isotopes

atoms (elements) with the same number of protons but different numbers of neutrons (different weights)

Plane Lattice

represent crystals by three integers (the Miller indices), where crystal structure intersects lattice axes

Bravais Lattice

all lattice points are equivalent, hence all atoms in the crystal must be of the same sort

Law of Bravais

faces on a crystal tend to be parallel to planes having a higher density of lattice points

P Lattices:

corner lattice point of unit cell. Primitive (simple)

C Lattices:

Center of certain faces. Base centered.

F Lattices:

Center of certain faces. Face centered.

I Lattices:

Center of the unit cell. Body-centered.

R Lattices

Rhombohedral (primitive)

Luster

the way light interacts with the surface of a mineral

Streak

the color of the mineral powder

Cleavage

a smooth break along specific internal planes

Fracture

breakage in random/rough patterns

Parting

when minerals break along planes of structural weakness due to external stress

Acicular

Crystal habit composed of slender, needle-like crystals

Oölitic

Crystal habit. Consists of small round grains cemented together (usually calcium carbonate)

Botryoidal

a mineral habit where the external structure is composed of rounded segments, originally meaning “bunch of grapes”. Ex: hematite

Malleable

the ability to be shaped under pressure without breaking

Coliform

spherical forms composed of radiating individuals w/out regard to size

Iridescence

as light touches the surface/interior at different angles, a series of colors are produced as the angle changes.

Conchoidal

sharp bright fracture of a mineral of which the surface is wavy.

Halide / Halogen

A halogen is a group 17 element (F, Cl, Br, I, etc.), a halide is an ionic compound formed from a halogen and a less electronegative element.

Alkaline Earth

Group 2 metals (Be, Mg, Ca, etc.)

Rare Earth Element

Consists of the lanthanoids (plus Yttrium & Scandium), and are rare heavy metals with similar chemical properties that are used in a variety of industrial applications

Transition Element

Groups 3-12 in the main series of the periodic table

Alkali Metal

Group 1 metals (Li, Na, K, etc.); characterized as being highly reactive

Phi (φ)

the angle for the distance around the outside of the stereonet

Rho (ρ)

angle of the distance from the center of the stereonet to a point