Identification of Minerals

Question 1

Observations during PPL

Answer 1

Opacity
Habit, Form, mode of aggregation
Color
Pleochroism
Cleavage

Question 2

Observations during XPL

Answer 2

Isotropic vs Anisotropic
Habit
Cleavage
Interference color
Sign of elongation
Extinction and ext angles
Twinning, zoning

Question 3

Function of the wavelength transmitted by the mineral

Answer 3

Color

Question 4

Color is best observed in?

Answer 4

PPL

Question 5

the ability of a mineral to absorb different wavelengths of transmitted light depending upon its crystallographic orientation.

Answer 5

Pleochroism

Question 6

Pleochroic hexagonal and tetragonal minerals

Answer 6

twofold pleochroism; dichroic

Question 7

exhibit varying degrees of absorption

Answer 7

Biaxial minerals

Question 8

Exhibit three different colors

Answer 8

trichroic

Question 9

darkest at long axis oriented perpendicular to polarizer

Answer 9

“normal” pleochroism

Question 10

darkest at long axis oriented parallel to polarizer

Answer 10

“reverse” pleochroism

Question 11

The degree to which mineral grains stand out from the mounting medium, have sharp boundaries, show fractures and cleavages well

Answer 11

Relief

Question 12

without regular crystal faces

Answer 12

anhedral

Question 13

has well-formed crystal faces

Answer 13

euhedral

Question 14

elongate needlelike grains

Answer 14

acicular

Question 15

elongate, slender

Answer 15

bladed

Question 16

shaped like a column

Answer 16

columnar

Question 17

equidimensional grains

Answer 17

equant

Question 18

individual grains are long slender fibers

Answer 18

fibrous

Question 19

flat elongate grains

Answer 19

lathlike

Question 20

the dominant faces are those of a prism

Answer 20

prismatic

Question 21

shaped like a book

Answer 21

tabular

Question 22

more or less parallel tabular or platy grains; flaky

Answer 22

foliated

Question 23

equant grains, all about the same size

Answer 23

granular

Question 24

elongate grains in a random pattern

Answer 24

matted

Question 25

elongate grains that radiate out from a center

Answer 25

radiating

Question 26

the way a mineral splits in preferred directions

Answer 26

Cleavage

Question 27

Things to do when looking for cleavage

Answer 27

Determine angle characterize if perfect, good, or weak/poor

Question 28

- Light rays are parallel to wave normal - Shows same velocity of light in all directions - Bonds are the same in all directons

Answer 28

Isotropic minerals

Question 29

- Light rays are not parallel to wave normal - Shows different velocity of light in all directions - Bonds are not the same in all directions

Answer 29

Anisotropic minerals

Question 30

The wavelength (color) exhibited by a mineral when viewed under XPL

Answer 30

Interference color

Question 31

dependent on orientation of mineral, or presence of cleavages of mineral grain

Answer 31

Extinction

Question 32

maximum interference angle that could be observed

Answer 32

45 degrees

Question 33

Monoclinic and triclinic minerals show what type of extinction

Answer 33

inclined extinction

Question 34

All uniaxial minerals show what type of extinction

Answer 34

Parallel extinction

Question 36

no cleavage to base extinction from

Answer 36

No extinction angle

Question 37

different parts of a grain becomes extinct at different angles

Answer 37

undulose/undulatory extinction

Question 38

The distance that one wave lags behind the other

Answer 38

Retardation

Question 39

Where i is an integer, then the two waves are said to be in phase

Answer 39

constructive interference

Question 40

two waves are said to be out of phase

Answer 40

destructive interference

Question 41

to determine which of the two rays coming through the mineral is the slow ray and which is the fast ray

Answer 41

sign of elongation

Question 42

fast ray direction

Answer 42

NW-SE

Question 43

slow ray direction

Answer 43

NE-SW

Question 44

3 ways to determine the sign of elongation

Answer 44

Orient the elongated mineral at 45 degrees CW Note interference color Engage compensator

Question 45

If increase in IC, mineral is length ____, or _____

Answer 45

length-slow; positive elongation

Question 46

If decrease in IC, mineral is ____; or_____

Answer 46

length-fast; negative elongation

Question 47

if mineral has 1 degree white gray IC, what plate should be used

Answer 47

mica plate

Question 48

color blind users use what plate

Answer 48

quartz wedge

Question 49

the intergrowth of two or more crystals in a symmetrical fashion by the sharing of lattice points in adjacent crystals

Answer 49

twinning

Question 50

changes smoothly from a more calcic core to a more sodic rim

Answer 50

normal zoning