(6) Identification of minerals

Question 1

. function of the wavelength transmitted by the mineral

. best observed in PPL

Answer 1

• color
• may be colorless, weakly colored or strongly colored

Question 2

the ability of a mineral to absorb different
wavelengths of transmitted light depending upon its ______

Answer 2

crystallographic orientation

Question 3

used to describe the color variation for
destructive interferencewith the polarization direction of the light, which depends on the
orientation of the material in the light path

Answer 3

Pleochroism

Question 4

colored uniaxial and biaxial are usually___

Answer 4

pleochroic

Question 5

twofold pleochroism or DICHROIC

Answer 5

Pleochroic hexagonal and tetragonal minerals:

Question 6

light vibrating at OA = color 1;
light at perpendicular to OA = color 2

Answer 6

Uniaxial minerals:

Question 7

exhibit varying degrees of
absorption

Answer 7

Biaxial minerals:

Question 8

exhibit three different colors; trichroic

Answer 8

Pleochroic orthorhombic, monoclinic and triclinic
minerals

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

Answer 11

Relief

Question 12

without
regular crystal faces

Answer 12

anhedral:

Question 13

has wellformed crystal faces

Answer 13

euhedral

Question 14

has
crystal faces but
they are poorly
formed or irregular

Answer 14

subhedral

Question 15

elongate needlelike grains

Answer 15

acicular

Question 16

elongate, slender

Answer 16

bladed

Question 17

shaped like a column; moderately
elongate grains with equidimensional cross
section

Answer 17

columnar

Question 18

equidimensional grains

Answer 18

equant

Question 19

: individual grains are long slender fibers

Answer 19

fibrous

Question 20

flat elongate grains

Answer 20

lathlike

Question 21

shaped like a book

Answer 21

tabular

Question 22

parallel arrangement of columnar
grains

Answer 22

columnar

Question 23

more or less parallel tabular or platy grains; flaky

Answer 23

foliated

Question 24

equant grains, all about the same
size

Answer 24

granular

Question 25

elongate grains in a random pattern

Answer 25

matted

Question 26

elongate grains that radiate out from a center

Answer 26

radiating

Question 27

-the way a mineral splits in preferred directions -represent planes of weak bonding in the mineral's atomic structure

Answer 27

Cleavage

Question 28

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

Answer 28

Isotropic materials

Question 29

examples of isotropic materials

Answer 29

isometric minerals and mineraloids

Question 30

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

Answer 30

anisotropic materials

Question 31

anisotropic materials example

Answer 31

minerals in tetragonal, hexagonal, orthorhombic, monoclinic, and triclinic systems

Question 32

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

Answer 32

Interference color

Question 33

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

Answer 33

Extinction

Question 34

All uniaxial minerals show what kind of extinction

Answer 34

parallel extinction

Question 35

Orthorhombic minerals show what kind of extinction

Answer 35

parallel extinction

Question 36

the crystal axes and indicatrix axes coincide

Answer 36

true (fun fact)

Question 37

Monoclinic and triclinic minerals have what kind of extinction

Answer 37

inclined extinctions

Question 38

FUN FACT

Answer 38

indicatrix axes **do not** coincide with crystallographic axes

Question 39

different parts of a grain become extinct at different angles

Answer 39

Undulose/undulatory extinction:

Question 40

: the distance that one wave lags behind the other (measured in nm)

Answer 40

Retardation

Question 41

Light rays travelling along the same path will in the same direction will____

Answer 41

interfere with each other

Question 42

tumaas yung interference color

Answer 42

constructive interference!

Question 43

two waves are said to be out of phase

Answer 43

destructive interference!

Question 44

If material with known retardation ΔA is superimposed over the mineral so that the slow ray vibration directions are parallel, the resulting slow ray and is further retarded

Answer 44

Higher interference color is produced

Question 45

If mineral’s fast ray is parallel to the slow ray of the material with known retardation ΔA, slow ray of mineral becomes fast ray in material with known retardation ΔA mineral’s fast ray is retarded

Answer 45

Lower interference color is produced

Question 46

The fast ray direction of the accessory plate is typically____

Answer 46

parallel to its length

Question 47

fast ray is

Answer 47

NW-SE

Question 48

slow ray is

Answer 48

NE-SW

Question 49

if mineral has 1° white-gray IC

Answer 49

use mica plate

Question 50

color blind users

Answer 50

use quartz wedge

Question 51

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

Answer 51

twinning

Question 52

changes smoothly from a more calcic core to a more sodic rim -core has a larger extinction angle

Answer 52

Normal zoning:

Question 53

alternation between calcic and sodic zones -usually from a more calcic core to a more sodic rim.

Answer 53

Oscillatory zoning: