guided notes on identifying minerals chapter 4, section 2

Guided Notes on Identifying Minerals

Chapter 4, Section 2

To identify minerals, geologists rely on several relatively simple tests, which are based on a mineral’s physical and chemical properties.

Color

What causes it? the presence of trace elements

How reliable is it? It is one of the least reliable clues to a mineral’s identity.

Luster

Definition:the way that a mineral reflects light from its surface

Two types: metallic and nonmetallic

What causes it? Differences in the chemical composition of minerals cause different lusters

Texture

Definition: how a mineral feels to the touch

Examples: fluorite has a smooth texture, talc has a greasy texture

Streak

Definition: the color of a mineral when powdered

How useful is it? It is one of the most reliable clues to a mineral’s identity

What are its limitations? It only works on minerals that are softer than porcelain

Hardness

Definition: how easily a mineral can be scratched

What causes it? Hardness is caused by the arrangement of a mineral’s atoms

How reliable is it? Hardness is one of the most reliable clues to a mineral’s identity

Cleavage

Definition: when a mineral splits evenly along one or more flat planes

What causes it? Weak atomic bonds in one or more direction

Examples: mica has perfect cleavage, halite has cubic cleavage

Fracture

Definition: breaking unevenly with rough edges

What causes it? Tightly bonded atoms

Examples: quartz has irregular fracture, flint has conchoidal fracture

Density

Definition: mass per unit of volume

What causes it? Differences in atomic weight and structure

How is it expressed? A ratio of mass divided by volume (g/mL)

Double Refraction

Definition: the refraction of a single ray of light into 2 images

What causes it? The arrangement of atoms in a mineral

Which minerals exhibit it? Calcite (Iceland Spar) and zircon

Magnetism

Which mineral exhibits it? magnetite

Describe how the Mohs scale of hardness is used…

Any mineral with a greater hardness than other mineral will scratch the softer mineral

The Mohs scale places common minerals in order of hardness, ranging from 1 to 10

Describe how scientists use specific gravity…

Specific gravity is the ratio of the weight of a substance to the weight of an equal volume of water.

Specific gravity is used as a measure of density because it contains easily understood numbers for comparison

A mineral is called an ore if it contains a useful substance that can be mined at a profit.

Ores located deep inside the earth are removed by underground mining. Ores near the surface are obtained from open-pit mines. If the cost of removing waste material from a mine becomes higher than the value of the mineral, then the mineral is no longer considered an ore.

Gems are valuable minerals prized for their rarity and beauty. The beautiful colors of gemstones are caused by the presence of trace elements.