physical properties of minerals

crystal habit/ shape

• angle of intersection of equivalent crystal faces are identical on all samples of a particular material

• Nicholas Steno

• “first law of crystallogrophy“

• can be unhelpful when minerals grow in masses

amorphous metals

• rigid substance BUT no ordered arrangement of atoms (NOT mineral)

• glass or obsidian

luster

• quality and intensity of light reflected from a mineral

• can be subjective

• metallic OR non-metallic

non metallic luster categories

• glassy/ vitreous

• dull or earthy

• greasy

• brilliant

colour of minerals

• results from the way they absorb/ transmit light

• can be very variable

• most unreliable characteristic

ferromagnesium silicates are always…

DARK (black, brown, green)

minerals with metallic luster have a more ….

consistent colour

streak test

colour of thin powder layer on a streak plate

• not used with silicates (most leave white)

• useful with oxides and sulfides

mohs hardness scale

scale of ten minerals used to compare hardness between the rest

• diamond = 10 (hardest)

• talc = 1 (softest)

cleavage

breakage or splitting of mineral crystals along a smooth plane

• # of planes determined by crystal structure

• can distinguish between minerals that otherwise look the same

• can further categorize by QUALITY of cleavage

basal cleavage

1 plane

prismatic cleavage

2 planes at a right angle

non-prismatic cleavage

2 planes NOT at right angle

cubic cleavage

3 planes at right angles

rombohedral cleavage

3 planes NOT at right angles

octohedral cleavage

4 planes of breakage

fracture

• irregular breakage of mineral

3 kinds of fracture

1. irregular

2. splintery

3. conchoidal (curved, as in broken glass)

a material that fractures could be

• a mineral with poorly defined cleavage (ex. olivine)

• a material with irregular distribution of atoms (ex. glass, obsidian)

density/ specific gravity

mass per unit volume

• ratio of weight of a mineral divided by weight of an equal vol of water @ 4 degrees C

optical properties

• opacity

• translucent/ not

if double refraction occurs, the mineral is always…

calcite!!