objectives define mineral and compare the two main groups identify the six types of silicate...

Objectives• Define mineral and Compare the two main groups

• Identify the six types of silicate crystalline structures.

• Describe three common nonsilicate crystalline structures.

• Describe seven physical properties that help distinguish one mineral from another.

• List five special properties that may help identify certain minerals.

Mineral Identification Basics• Mineral: neral: a solid with an orderly a solid with an orderly

internal structureinternal structure

• To be a mineral, a substance To be a mineral, a substance must have must have 4 characteristics:4 characteristics:

1.1. must be inorganicmust be inorganic—not —not made of living thingsmade of living things

2.2. must occur naturallymust occur naturally——not man-madenot man-made

3.3. must be a crystalline must be a crystalline solidsolid

4.4. must have a consistent must have a consistent chemical compositionchemical composition

Cubic Fluorite Crystal

Characteristics of Minerals

The diagram below shows the 4 characteristics of minerals

Silicate Minerals• All minerals can be classified

into two main groups—silicate minerals and nonsilicate minerals

• Silicate mineral: a mineral which contains silicon and oxygen, and may contain one or more metals– Common silicate minerals

include quartz, feldspars, and micas

– Silicate minerals make up 96% of Earth’s crust. Quartz and feldspar alone make up more than 50% of the crust.

Nonsilicate Minerals• Nonsilicate mineral: a

mineral that does not contain silicon and oxygen– comprise about 4% of

Earth’s crust– organized into six major

groups.

1. Carbonates2. Halides3. native elements4. Oxides5. Sulfates6. sulfides

Crystalline Structure• Crystal: a solid whose

atoms, or molecules are arranged in a regular, repeating pattern

• Each mineral has a specific geometric arrangement of atoms, also known as its crystalline structure.

• Scientists study the structure of crystals using X rays. These produce an image which shows the geometric arrangement of atoms in the crystal.

Physical Properties of Minerals• Mineralogist: a person who

examines, analyzes, and classifies minerals

• Each mineral has specific properties, which are the result of its composition and crystalline structure. These properties provide useful clues for identifying minerals.

• The 6 properties used to classify minerals are:

1. Color2. Streak3. Luster4. Cleavage5. Fracture6. Hardness

Color

• Color: most noticeable property, but least-accurate method for identifying a mineral

Many minerals have similar colors

Streak

• Streak: color of a mineral in powdered form• More reliable than color

for mineral identification• Determined by rubbing

the mineral against a streak plate

• The streak is often different from the apparent color of an unground sample

• The streak color of a mineral will always be the same, even it its external color varies

Most metallic minerals have a dark streak

Magnetite

Galena

Chalcopyrite and Galena

Graphite

…while most nonmetals have a light streak

calcite

Peridot (polished)

Amethyst

Citrine

Luster

• Luster: The quality and intensity of light reflected from the surface of a mineral

• Luster is either metallic or nonmetallic

Metallic Luster• Metal-like shine• Dark Streak

Nonmetallic Luster

• More common• Light streak color

Cleavage and Fracture• Cleavage: tendency of a mineral

to split• Occurs due to weakness in structure

of mineral

• Fracture: the way a mineral breaks along either curved, or irregular surfaces

• Uneven or irregular fractures have rough surfaces.

• Curved fractures are smooth

Hardness• Hardness: measure of

resistance to scratching

• A harder substance will scratch a softer substance

• Hardness can be determined by comparing the mineral to those on the Mohs hardness scale ->

Mohs Hardness Scale

Magnetism

•Magnetism: ability of a mineral to act as a magnet

•Most commonly associated with minerals rich in iron

•Minerals rich in iron are called magnetites

•Iron is highly magnetic…remember this!

This is a piece of iron with a magnet attached

Magnetism

This is a sample of “black sand” from Lynx Creek, Arizona. Its dark color is due to its high concentration of magnetite. See what happens when a magnet is place beneath the bottom right portion of the paper?

This technique is used to separate out much of the unwanted material in the search for gold.

Magnetism

Lodestone is a variety of Magnetite which is a

natural magnet.

Fluorescence

• A few minerals have some additional, special properties

• The ability to glow under ultraviolet light is called fluorescence.

• Fluorescent minerals absorb ultraviolet light and then produce visible light of various colors.

Willemite