Download Minerals

Minerals
What are minerals?
• Rocks are made up of one or more pure, naturally
occurring, crystalline materials called minerals
• Most minerals are quite rare
• Only a few, such as quartz, feldspar and mica are
found throughout the Earth’s crust
• A mineral can be an element (think periodic table)
or a compound (two or more elements)
Examples
Quartz, a very common
mineral, is made of silicon
and oxygen
Granite rock (shown to the
right) is made of an
assortment of minerals,
including quartz (glassy
grains), feldspar (sparkling
grains), mica (grey flakes),
and hornblende (dark
flecks)
Ways to Identify Minerals
• Mohs Scale of Hardness
• You can think of Friedrich Mohs scale as a
scratchability test
• It helps identify minerals based on their hardness
• Check out the scale on the next slide
Mohs Scale of Hardness
Crystals
• There are over 3000 minerals
• Crystals are the building blocks of minerals
• Crystals occur naturally and have straight edges, flat
sides and regular angles
• Most minerals grow into specific crystal shapes
according to the systems chart on the next slide
Crystal Systems
Lustre
• Some minerals like gold and other metals, appear
shiny – another way to identify them
• Other minerals like talc, can appear dull
• The “shininess” or lustre, of a mineral depends on
how the light is reflected from its surface
• Shiny surface are said to have “metallic” lustre while
dull surfaces are said to have non-metallic lustre
Colour
• The colour of a mineral can also be used as a clue to a
mineral’s identity
• However, colour alone cannot identify a mineral
• Some minerals like gold and pyrite are both “goldcoloured”
• Some minerals are not the same colour all the time
• Corundum is white when pure, but blue when it contains
iron or titanium (called a sapphire), and when it has
chromium it is red (called a ruby) see next slide
Misleading Colour
Streak
• When a mineral is rubbed across a piece of unglazed
porcelain tile, it leaves a streak
• Streak is the colour of the powdered form of the mineral
• Look-alikes, such as gold and pyrite, can be distinguished
from each other by their streak – gold leaves a gold streak
and pyrite leaves a greenish-black or brown-black streak
• Minerals with a hardness greater than the tile will not
leave a streak
Streak (cont.)
Hematite can by
dark red, grey or
silvery in colour
However, its streak
is always dark redbrown
Cleavage and Fracture
• The way a mineral breaks apart can be a clue to its
identity
• If it breaks along smooth, flat surfaces, or planes, it
is said to have cleavage
• Mica is a good example of a mineral with cleavage
• Minerals that break with rough or jagged edges have
fracture
• Quartz is an example of a mineral with fracture
Cleavage & Fracture (cont.)
Mica
Quartz