IDENTIFYING MINERALS
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