IDENTIFYING MINERALS

IDENTIFYING MINERALSMinerals can be identified by inspecting them visually to determine physical properties and by performing tests to determine chemical properties

Rarely is a mineral identified by a single property

Crystal formLusterHardnessCleavage

FractureStreakColourTexture

Density Specific GravitySpecial Properties

CRYSTAL FORM

Crystal form - visible expression of a mineral’s internal arrangement of atoms

Crystal faces can be difficult to find, and don’t always form

COLOUR

Colour - some minerals have distinctive colours

Trace elements within mineral determine colour - some minerals have multiple colours

Least reliable

Varieties of Quartz

TEXTURE

Texture - how mineral feels to the touch

Common textures: smooth, rough, ragged, greasy or soapy

Fluorite - smooth Talc - greasy

LUSTERLuster - way a mineral reflects light from its surface

Two types: metallic and non-metallic

Metallic luster - shiny

Non-metallic - dull, pearly, waxy, silky, earthy, glassy

Chalcocite

Feldspar

STREAKStreak - colour of mineral when broken up and powdered

Streak is not always same colour as mineral

Hematite - look different, but same composition so same streak

CLEAVAGE

Cleavage - tendency of a mineral to cleave or break easily along flat, even surfaces where atomic bonding is weak

Not all minerals exhibit cleavage

Biotite

Calcite

FRACTURE

Fracture - when minerals break unevenly along jagged edges because of tightly bonded atoms

Aquamarine

HARDNESSHardness - measure of how easily a mineral is scratched

10 point Mohs hardness scale - increase in hardness is not uniform

Diamond is hardest mineral, talc is softest

Amythest

MOHS HARDNESS SCALE

Diamond

Talc

DENSITY

Density - mass per unit volume

Density reflects atomic mass and structure of mineral, not size or shape

Differences in density are too hard to distinguish simply by lifting minerals, so it must be measured by determining specific gravity

D = M V

SPECIFIC GRAVITY

Specific gravity - ratio of mass of a substance to mass of an equal volume of water at 4oC

Tells you how many times denser a mineral is than water

Minerals are denser than water, so specific gravity is greater than 1

Azurite

Dioptase

SPECIAL PROPERTIES

Fluorescent - glow when exposed to UV light

Magnetic - occurs in minerals that contain iron; attracted by a magnet

Double Refraction - ray of light passes through mineral and is split into two rays

Effervescence - reacts with HCl to create fizz