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.
