Transcript Mineral and Rock Properties

Mineral and Rock Properties
©2010 Dr. B. C. Paul
Note most of the material for these slides was collected from a wide range of
available sources and do not represent the organizers original work.
Difference Between Minerals and
Rocks
• Mineral has the same composition (atoms of
different kinds) and structure (arrangement of
those atoms) all the way through.
– About 3,000 known minerals
• Thank goodness you will not be ask to learn them all – We
are interested in the ore minerals
• Rock is made up of 2 or more different minerals
– Remember your igneous rocks had more or less of
the dark minerals depending on the iron content
Destructive and Non Destructive
• Many characteristics depend on fresh
unweathered surfaces to see
– If you try breaking the class samples I’ll get irate
– I’m not going to push things like crystal form because
a lot of ore deposits are massive or crystal structures
are very small
• Are tests like looking at color and luster, feeling
how heavy it is, or checking with a magnet or
fluorescence that do not hard the specimen
Rock Density
• Some Rocks are Heavy for their Size –
Some are Light
• Density or Specific Gravity
– Water at near freezing temperature is given a
specific gravity of 1 (62.428 lbs/cubic foot)
– Specific Gravity of a Mineral is Ratio of the
weight of 1 unit of the mineral to one unit of
water
Examples
You can use this to help clue you in on what mineral you may have by
How heavy it is.
Hardness
• How Easy it is to
scratch and what will
scratch it.
• Mohs Hardness Scale
Talc =1
Gypsum =2
--fingernail at 2.5
Talc
Gypsum
More Hardness
Calcite =3
--copper (old penny) at 3.5
Mohs Hardness Scale Continued
Fluorite =4
Apatite =5
--window glass or typical
knife blade at under 5.5
Fluorite
Apatite
The Hardness Scale
Orthoclase
--streak plate or good steel file at over
6.5
Really Hard Stuff
Quartz =7
Topaz = 8
Corundum = 9
Diamond = 10
Quartz
Topaz
Diamond
Mohs Hardness Scale is Relative –
Not Absolute
Color
Actually less useful than you would hope because you can throw mineral colors
A great deal with simple impurities – can be a hint when used with how shiny or
Clear it is. Also some things can have pretty distinctive colors
Streak
Streak is closely related to color, but is a different property because the color of the
mineral may be different than the color of the streak. Streak is actually the color of
the powder of a mineral. It is called streak because the proper way to test for streak
is to rub a mineral across a tile of white unglazed porcelain and to examine the color
of the "streak" left behind. It has proven to be a powerful property because it is
generally very consistent from specimen to specimen for a given mineral.
Its kind of a tie breaker because only 20% of minerals have a unique streak
(but a lot of those that do are ore minerals)
When Exposed to Short Wave Light
Many Minerals Develop Unique
Glows
Property is Called Luminescence
• Minerals contain certain elements that are
called “activators”
• Electrons in the activator element can be
bounced up into higher electron shells
– When they drop back down they put out a
unique colored glow.
• If the something that bounces electrons up
into higher shells is light we call it
“Fluorescence”
The Light Spectrum
Real short
Wave stuff
Will make
You glow in
The dark too
(of course
You’ll also die)
Most Fluorescence is to light or the wrong color for us to see
Things that Can Build Distinct
Fluorescence
• X-Rays are great
• (of course X-Ray machines aren’t very
cheap and you really can’t be around them
much – back to the you glow and die
problem)
• Ultraviolet Light Will Work on a Lot of
Minerals.
UV Light
We call this Black Light
(probably have had some fun with it)
It will activate about 15% of Fluorescent
Minerals
The Short and Midrange UV will activate
90% (and also Sun-Burn you)
UVA
UVB
UVC
Some Typical Fluorescent Minerals
More Fluorescence
Magnetic
• Not a lot of minerals attracted to magnet
• Most of them that are are ore minerals
• Many minerals are only weakly magnetic
so it takes a fairly impressive magnet to
pull them