MINERALOGY - TERMS/CONCEPTS (REVIEWER FOR FINALS)

Crystals

They are formed from solution, melts, and vapors.

Pressure

Temperature

Concentration

What are the 3 Factors of crystallization?

Nucleation

It is the initial stage of crystal growth. It forms nucleus as a result of chemical bonding of various ion.

Formation of crystal structure/crystal faces

It is a result of the continuous growth from a nucleus that exhibits highly-ordered crystalline structure.

Formation of Euhedral Crystal

It is a result of the continuous growth of a nucleus that exhibits euhedral crystal - well-defined crystal boundary.

Intergrowths of Crystals

It refers to the occurrence of one or more crystals in the same mineral.

Crystal Twinning

Other term for intergrowth of crystals:

Crystal Twinning

Sometimes during the growth of a crystal, or if the crystal is subjected to stress or temperature/pressure conditions different from those under which it originally formed, two or more intergrown crystals are formed in a symmetrical fashion.

Reflection

Rotation

Inversion

What are the 3 symmetry Operations that Define Twinning?

Twin plane

Reflection across a mirror plane. The added mirror plane would then be called a _______________.

Twin Axis

Rotation about an axis or line in the crystal. The added rotation axis would then be called a ____________.

Twin Center

Inversion through a point. The added center of symmetry would then be called a _____________.

Twin laws

Are expressed as either form symbols to define twin planes (i.e. (hkl]) or zone symbols to define the direction of twin axes (i.e. [hkl]).

Composition surface

The surface along which the lattice points are shared in twinned crystals is called a __________________.

always parallel

never parallel

the twin plane is _____________________ to a possible crystal face and ______________________ to an existing plane of symmetry (remember that twinning adds symmetry).

Contact Twins

They have a planar composition surface separating 2 individual crystals.

Contact Twins

Are usually defined by a twin law that expresses a twin plane (i.e. an added mirror plane).

Penetration Twins

They have an irregular composition surface separating 2 individual crystals.

Penetration Twins

These are defined by a twin center or twin axis.

Polysynthetic Twins

Twins whose composition surfaces are parallel to one another.

Cyclical Twins

Twins whose composition surfaces are not parallel to one another

Albite Law

- Type of polysynthetic twinning (e.g., plagioclase)

- The twin law [010] indicates that the twining occurs perpendicular to the b crystallographic axis.

Albite Law

Is a type of crystal twinning, specifically in plagioclase feldspars, characterized by parallel, thin lamellae (striations) on the basal plane.

Pericline Law

It describes a specific type of crystal twinning where the twin axis is the b-axis, typically occurring in microcline feldspar.

Pericline twinning

It occurs as the result of monoclinic orthoclase or sanidine transforming to microcline. It usually occurs in combination with albite twinning in microcline but is only observable with the polarizing microscope.

tartan twinning

The combination of pericline and albite twinning produces a cross-hatched pattern, called __________________.

Manebach Law

- Type of contact twinning

- It forms a contact twin commonly observed in the mineral orthoclase.

- This twinning is very diagnostic of orthoclase when it occurs.

Carlsbad Law

- Type of penetration twinning

- It shows two intergrown crystals, one rotated 180º from the other about the [001] axis.

Carlsbad twinning

Is the most common type of twinning in orthoclase and is thus very diagnostic of orthoclase when it occurs.

Braveno Law

This type of twinning occurs in minerals like orthoclase, where two intergrown crystals are separated by a planar surface.

Baveno Law

- Type of contact twinning

- Twin plane at {021}

Swallowtail Law

- Type of contact twinning

- Twin plane at {100}

- Commonly occurred in gypsum

Staurolite Law

Occurring in monoclinic mineral but has an appearance of an orthorhombic minerals.

Calcite Law

Occurs as polysynthetic twins that result from deformation.

calcite crystals.

The two most common twin laws that are observed in ___________________.

Brazil Law

Occurs at {112̅ 0} - is a penetration twin that results from transformation.

Dauphine Law

Occurs at [0001} - is a penetration twin that results from transformation.

Japanese Law

Occurs at {112̅ 2} - is a penetration twin that results from accidents during growth.

Spinel Law

It is a twin plane at {1̅ 1̅ 1}, parallel to an octahedron that occurs commonly in mineral spinel.

Iron Cross Law

The mineral pyrite (FeS₂) often shows the iron cross made of the interpenetration of two pyritohedrons.

Mineral Stability/Phase Diagram

It is a graphical representation of chemical equilibrium that shows the behavior of solids, liquids and gases under variable external condition, such as those of temperature and pressure.

external conditions

Phase diagrams are very useful in providing a visual image of what a mineral or group of minerals is stable with respect to some other mineral or mineral groups at a specific set of ___________________.

Lever Rule

A mathematical expression by which the relative phase amounts in a two-phase alloy at equilibrium may be computed.

Physical Properties

It is fundamentally controlled by the crystal structure and chemical composition of the mineral

Interaction with Light

Mass-Dependent Properties

Shape

Properties Related to Mechanical Cohesion

Magnetic and Electrical Properties

What are the 5 Common Physical Properties of minerals?

Color

Luster

Streak

Luminescence

Diaphaneity

Common Physical Properties under Interaction with Light:

Visible Light

A segment of the electromagnetic spectrum that the human eye perceives.

Monochromatic Light

Consists of a single wavelength as one of the spectral colors

Polychromatic Light

Consists of more than one wavelength

Complementary Colors

Refers to the combination of two colors

Mineral Color

Refers to our perception of wavelengths of light that are reflected from or refracted through the mineral

Selective absorption

Process by which a material absorbs some components of visible light and transmits others.

Selective absorption

Describes how electrons in each atom in the crystal structure interact with light

Impurities

Refers to the elements (e.g., Ti, V, Cr, Mn, Fe, Co, Ni, Cu...) that are not present in the pure compound.

Corundum (Al2O3)

(1) Mineral Color: Colorless

Ruby (Al2O3 Cr)

Mineral Color: Pinkish Red to Blood Red

Sapphire (Al2O3 Fe, Ti)

Mineral Color: Blue

Amethyst (SiO2. Fe³)

Mineral Color: Purple

Quartz (SiO2)

(2) Mineral Color: Colorless

Tarnish

It is a property in certain minerals that cause them to discolor when placed in certain environments.

Diaphaneity

Refers to a mineral that can transmit light

Opaque

Impossible to see through; no light is transmitted

Translucent

when light, but not an image is transmitted

Transparent

When both light and image are visible

Luster

It refers to the general appearance of the mineral surface in reflected light

Metallic

minerals that have the appearance of a metal

Submetallic

minerals with a metallic appearance but develop a dull coating or tarnish

Non-Metallic

minerals that do not have the appearance of a

metal

Vitreous

Minerals that exhibit glassy appearance

Resinous

Minerals that appear like resin

Pearly

Minerals that appear like pearls where their surfaces are parallel to well-developed cleavage planes

Greasy

Minerals that appear as though covered with a thin layer of oil which results from light scattered by microscopically rough surfaces

Silky

Minerals that exhibit a skein of silk or a piece of satin which are characteristics of some fibrous minerals

Earthy

Minerals that have dull surfaces that lack any shine and are generally seen with aggregates of very fine mineral grains

Adamantine

Minerals that appear with brilliant luster like glass commonly exhibited by minerals harder than the streak plate

Streak

Describes the color of the mineral in powdered form and can also help distinguish between minerals with metallic and nonmetallic luster

dense, dark

light-colored

Metallic minerals have a _______________ streak.

Nonmetallic minerals have a ___________ streak

Play of Colors or Iridescence

Refers to the series of colors due to the interference of light either at the surface or in the interior of a mineral as the angle of the incident of light changes

Adularescence (Schiller)

It is best described as a milky, bluish luster or glow originating from below the surface of the mineral

Labradorescence

Refers to a peculiar reflection of the light from sub-microscopical planes orientated in one direction (rarely in two directions)

Aventurescence

Refers to a metallic glitter, arising from minute, preferentially oriented mineral platelets within the mineral

Chatoyancy or AKA Cat's Eye Effect

It shows a band of light at right angles to the length of the fibers or the direction of the inclusion which commonly occurring on fibrous minerals with closely packed parallel fibers or from a parallel arrangement of inclusions or cavities.

Asterism

- Crystals that exhibit triple chatoyancy, that is, one beam of light at right angles to each direction of the inclusions producing a six-pointed star which is a result of the scattering of light from inclusions of rutile arranged in three crystallographic directions.

Luminescence

Refers to the emission of light by a mineral that is not a direct result of incandescence

impurity ions activators

Luminescence is usually observed in minerals containing __________________ and can only be seen in the dark.

Fluorescence

It is where the energy is supplied by electromagnetic radiation typically caused by UV light

Phosphorescence

Refers to the delayed luminescence or "afterglow".

Density

Specific Gravity

Common Physical Properties under Mass-Dependent Properties:

Density

Refers to the mass of the mineral per unit volume

Specific Gravity

Refers to the ratio of the density of the mineral to the density of water (~1.0 g/cm³)

Crystal Form

It consists of a group of crystal faces, all of which have the same relation to the elements of symmetry

Euhedral

It describes a mineral that is completely bounded by crystal faces and whose growth during crystallization was not restrained or interfered with by adjacent crystals or mineral grains

Subhedral

It describes a mineral grain that is partly bounded by crystal faces and partly by surfaces formed against preexisting grains

Anhedral

It describes a mineral that lacks crystal faces and that may show rounded or irregular surfaces produced by the crowding of adjacent minerals during crystallization

Habit

It describes the general shape and irregularities of the crystal

Crystal Habit

Describe the shape of each crystal

Aggregate Habit

Describe the shape of the group or assemblage of similar crystals

Fibrous

Parallel arrangement of acicular or filiform crystals

Radiating

Acicular-filiform crystals radiating outward from a central point

Divergent

Prismatic crystals diverging from a common area