Properties of Minerals
What is a Mineral?
Minerals are naturally occurring.
Minerals have a crystal
structure and definite
chemical composition.
Minerals are solids.
Minerals are inorganic; not
ever part of a living thing.
• The visual description of the mineral overall
• The same mineral can be many colors!
These minerals are ALL forms of quartz! Color alone is not a reliable way to describe minerals.
• Exposure to environment or chemicals may change the
color of minerals.
Pyrite turns grey and black.
Oxidation turns iron from
silver to black to red!
Copper turns green!
Color is not a reliable property to use in the identification of minerals!
Luster:
the way a mineral reflects light from the surface
• plastic, dull, metallic, waxy, pearly, glassy, silky, earthy
Waxy or greasy, pearly
dull
glassy
glassy
metallic
resinous, plastic
earthy
silky, fibrous
Streak
• Powder made from rubbing a mineral across a
streak plate; sometimes shows a different color
than the mineral appears to be.
• Shows a mineral’s true color (Reliable!)
Pyrite
Galena
Hematite
Cleavage
• Minerals that break easily along flat surfaces
have cleavage.
Types of Cleavage
Do I have to know all of these? NO! Just be able to identify cleavage as having flat sides
Fracture
• break along curved or irregular surfaces
Fibrous, like strings
Conchoidal, “shell-shaped”
Irregular, chunky
Crystal Structure
• Atoms in a mineral line up in a repeating pattern
• Classified by the number of faces or sides and the
angle at which the faces meet
• Examples: Halite = cubic (isometric)
Quartz = hexagonal
Which ones do I need to know? Cubic (not the term isometric) and Hexagonal
Hardness
• is the resistance to being scratched
• can be measured using a scratch test:
• using Mohs Hardness Scale, which compares
minerals to each other
• using common items such as a fingernail,
copper penny, steel knife blade, glass
A fingernail can scratch talc.
Quartz can scratch glass,
but fluorite cannot.
Mohs Hardness Scale
Hardness
Density
• How much mass there is in a given space, or
mass per unit volume
• Density = Mass divided by Volume
• Volume is determined using the displacement method;
dropping the mineral in water and seeing how much it
has moved up from the original amount.
volume
mass
The density of a substance is described as the amount of matter
(mass) that is contained in a given volume. You can see by the pictures
that some materials are more dense than others because of the
amount of space that is between their particles (atoms and molecules),
and by comparing the size of the atoms or molecules that are packed
into the same size space (volume).
Special Properties
Magnetism
Fluorescence
Reactivity
Radioactivity
Salty Taste
But NEVER taste things in the lab!
Odor
Double Image