Transcript Minerals

Minerals
Minerals
Minerals are solid, inorganic substances
found in the Earth’s crust.
What is a Mineral?
Characteristics of Minerals:
 Naturally Occurring
 Inorganic
 Solid
 Definite Chemical Formula
 Definite Crystal Structure
Naturally Occurring

Formed by natural processes (not in the
laboratory).
- Is an ice cube a mineral?
- Is the ice on the windshield of a car a
mineral?
Inorganic

Formed by inorganic processes; not living.

Does not contain chains of carbon atoms.
Solid

Not gas or liquid.
-H2O as ice in a glacier is a mineral, but
water is not.

Definite volume and shape.
Definite Chemical Formula

Minerals are expressed by a specific
chemical formula:
-Gold (Au)
-Calcite (CaCO3)
-Quartz (SiO2)
-Pyrite
(FeS2)
Definite Crystal Structure


A crystal is a solid in which the atoms are
arranged in repeating patterns.
Some mineral specimens have
flat surfaces and sharp edges,
showing distinct crystal shapes
on the outside.

Even if a mineral doesn’t show
its crystal shape on the
outside, its atoms are still
arranged in an orderly crystal
structure.
Composition of the Earth’s Crust
 An element is made of one atom and a Compound is
two or more elements together
 Eight Elements make up over 98% of Earth’s Crust:
-Oxygen (O) 46%
-Silicon (Si) 28%
-Aluminum (Al)
-Iron (Fe)
-Calcium (Ca)
-Sodium (Na)
-Potassium (K)
-Magnesium (Mg)
 Minerals are always single chemical compounds or
pure elements.
Where Do Minerals Come From?
Magma
Evaporation
Of the almost 4000 known minerals,
only about 100 are common.
The most common are
quartz,feldspar,mica, and calcite.
How Are Minerals Identified?









Color
Texture
Luster
Hardness
Streak
Heft
Crystal Form
Cleavage and Fracture
Special Properties
Color


Usually the first and most easily observed.
Sometimes very helpful for ID, sometimes
not much help at all.
-Some minerals are always the same color (malachite = green, azurite = blue).
-Some minerals can have many colors (quartz = white, clear, purple, pink, yellow, gray).
ROSE QUARTZ
QUARTZ
SMOKY QUARTZ
Texture

How a mineral feels to your touch.
-For example:
Some minerals feel greasy or soapy.
Luster


General appearance of a mineral surface in reflected light.
Minerals can be classified as either metallic or non-metallic
luster.
Glassy-Obsidian
Luster

Non-metallic luster can be broken down into
several types:
-Glassy (Vitreous)– looks like glass.
-Silky – shines like a silk cloth.
-Pearly – looks like pearls.
-Adamatine – brilliant, diamond-like shine.
-Greasy – looks like its covered with oil.
-Dull/Earthy – no apparent “shine”.
Hardness

Resistance to scratching by different items;
“scratchability”.
Mohs Hardness Scale
2.5
3.5
4.5
~5
5.5
6.5
7
Fingernail
Penny
Nail
Steel of a pocket knife
Window Glass
Steel file
Quartz crystal
Ex: If an unknown mineral can scratch a penny but can’t scratch glass, we
would say its hardness is between 3.5 and 5.5
Mohs Mineral Hardness Scale
1) Talc
Softest
2) Gypsum
3) Calcite
1
8
4) Flourite
5
5) Apatite
2
6) Feldspar
7) Quartz
9
6
8) Topaz
3
9) Corundum
10) Diamond
7
Hardest
4
10
Streak



The color of a finely powdered mineral.
Determined by rubbing the mineral on a
streak plate.
It may or may not be the same color as
the mineral
Heft

The amount of matter in a given space.

Mass/Volume = Density.
Crystal Form



Minerals have a characteristic crystal
shape resulting from the atomic packing of
the atoms when the mineral is forming.
The shape of crystals, if present, can be
very helpful in ID.
A mineral sample often may not have
crystals large enough to see.
Cleavage and Fracture



How a mineral breaks:
Cleavage is the tendency of a mineral
to split or crack along parallel or flat
planes (even breaking).
Fracture occurs when a mineral breaks
at random lines instead of at consistent
cleavage planes. (uneven breaking).
Special Properties





Magnetism (Magnetite)
Glowing under ultraviolet light (Fluorite)
Salty taste (Halite)
Magnetite
Smell (Sulfur)
Reaction to HCl (Calcite)