MINERALS IN PPL

Question 1

ppl

Answer 1

plane-polarised light

Question 2

optical properties in ppl

Answer 2

transparent/opaque

crystal size/shape

cleavage or fracture

colour

relief

Question 3

optical properties in ppl: transparent/opaque

Answer 3

transparent, appears white

opaque, appears colourless grey
tends to be oxides, such as chromite

Question 4

optical properties in ppl: crystal size/shape

Answer 4

euhedral, well-shaped

subhedral, moderately well-shaped

anhedral, no crystal faces developed

Question 5

optical properties in ppl: colour

Answer 5

coloured minerals often rich in iron

if colour changes as mineral rotated in ppl, mineral said to be pleochroic

Question 6

optical properties in ppl: relief

Answer 6

describes surface appearance of mineral in ppl

mineral with refractive index different from mounting medium appears to be ‘standing out’ from slide, high relief

mineral has high birefringence, relief varies as stage rotated

Question 7

Birefringence

Answer 7

formally defined as double refraction of light in transparent, molecularly order material