Mineralogy Midterm

True or False?

Most minerals have a single cation or cationic group, while they often have more than one anion.

False.

Most minerals have a single anion or anionic group, while they often have more than one cation.

Crystal Chemistry

relationship of chemical composition to atomic structure

Mineral

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

Steno’s Law

"In crystals of the same species (different specimens), under equal conditions of pressure and temperature, the corresponding dihedral angles are always the same, the number, shape and size of the faces being variable"

The 5 chemical bonds

ionic

covalent

metallic

van der waals

hydrogen

Compounds ending in–ide…

are simple binary compounds containing 2 elements even if there is no metal

Compounds ending in–ate…

means oxygen is present

Ending in –ite…

have less oxygen present than in –ate compounds

4 Crystal Bonding Types

1. Molecular Crystal

2. Covalent Crystal

3. Metallic Crystal

4. Ionic Crystal

radius ratio

is the ratio of the cation radius to the anion radius

symmetry

Property that makes an object (motif) coincide with another identical one through a movement called the symmetry operation

4 Basic Symmetry Operations

Translation

Rotation

Reflection

Inversion

6 Crystal Systems

Triclinic

Monoclinic

Orthorhombic

Tetragonal

Hexagonal

Isometric

Crystal shape is determined by _______

Atomic arrangement

THE BECKE LINE WILL ALWAYS MOVE ONTO THE MATERIAL WITH THE________ AS THE STAGE IS LOWERED

HIGHER REFRACTIVE INDEX

When the RI of the mineral and the RI of the mounting material are equal, the Becke line…

splits into two lines, a blue line and an orange line.

Anisotropic minerals extinct _____ times

4

Isotropic minerals extinct ___ times

Isotropic minerals are always extinct. This is because they cannot reorient light

What causes extinction?

The direction of vibration of light in the mineral is parallel to the direction of polarization

Uniaxic crystal systems

Hexagonal

tetragonal

biaxic crystal systems

rhombic, monoclinic, triclinic

C axis refers to the…

Optic axis

All uniaxial minerals show ____ extinction

parallel

What type of interference figure is this + label the elements

Centered Uniaxial Interference Figure

Isochrome: pattern of interference colours that are identical to those on the colour chart, increase in order from the melatope

Isogeres: Two arms of the cross

Melatope: The point where the optic axis emerges in the interference figure; it corresponds to 0 retardation

The 3 Uniaxial Interference Figures

Optic Axis Figure-OA vertical

Off Centred Optic Axis Figure- OA inclined

Flash Figure- OA horizontal

Which quadrant helps you determine the sign?

The NE quadrant

Label 1-5

1. Optic Axis

2. Z axis

3. Optic Axis

4. Y

5. X

direction X = ?

direction Y = ?

direction Z = ?

1. direction Z = nγ (highest)

2. direction X = nα(lowest)

3. direction Y = nβ (intermediate; ray of circular section)

How is 2V measured?

Using the interference figures

Bxa stands for…

Acute Bisectrix

OA stands for…

Biaxial Optic Axis

Bxo stands for…

Obtuse Bisectricx

ON stands for…

Biaxial Optic Normal or Flash Figure

The appearance of the interference figure is dependent on the ____ of the mineral grain and its corresponding______

orientation ; indicatrix

Isotropic

speed of light is the same in any direction.

Vibration direction will always be perpendicular to the propagation direction

only ONE index of refraction

Anisotropic

speed of light varies depending on the direction the light is traveling in

more than one index of refraction

“Cross Nichols” refers to…

adding the analyzer (XPL)

Pleochrism

minerals ability to change its color when its position is changed on the stage

The slow ray in an anisotropic mineral will have a _____ than the fast ray

higher index of refraction

The fast ray is the ______ and is _______ when going through the mineral

extraordinary ray ; not deviated

The slow ray is the ______ and is _______ when going through the mineral

ordinary ray ; slowed down + deviated

the sign of elongation is POSITIVE if the ____ beam vibrates ____ to the maximum length of the crystal

slow ; parallel

the sign of elongation is NEGATIVE if the ____ beam vibrates ____ to the maximum length of the crystal

fast ; parallel