1. Section 2: Identifying Minerals
Introduction
This section identifies the major properties and crystal systems of minerals.
It also explains special properties that help in the identification of minerals

2. 6. Physical Properties of Minerals
Earth scientists called mineralogists examine, analyze, and classify minerals
To identify minerals, mineralogists study the properties of the minerals.
Each mineral has specific properties that are a result of its chemical composition and crystalline structure.
These properties provide useful clues for identifying minerals.
Many of these properties can be identified by simply looking at a sample of the mineral.
Other properties can be identified through simple tests.

3. Physical Properties of Minerals (cont.)
Color
Some minerals have very distinct colors
Color alone, however, is generally not a reliable clue for identifying a mineral sample.
Many minerals are similar in color, and very small amounts of certain elements may greatly affect the color of a mineral.
Weathered surfaces may hide the color of minerals
When examining a mineral for color, you should inspect only the mineral’s freshly exposed surfaces.

4. Physical Properties of Minerals (cont.)
Streak
A more reliable clue to the identity of a mineral is the color of the mineral in powder form, which is called the mineral’s streak
The easiest way to observe the streak is to rub some of the mineral against a piece of unglazed ceramic tile called a streak plate
The streak’s color may differ from the color of the solid form of the mineral.
Minerals that are harder than the streak plate will leave no mark

5. Physical Properties of Minerals (cont.)
Luster
Light that is reflected from a mineral’s surface is called luster.
Two main types of luster: metallic and nonmetallic
Many different types of nonmetallic luster
Glassy
Waxy
Pearly
Brilliant
Dull/Earthy

6. Physical Properties of Minerals (cont.)
Cleavage and Fracture
The tendency of a mineral to split along specific planes of weakness to form smooth, flat surfaces is called cleavage.
Many minerals fracture, or break unevenly, into pieces that have curved or irregular surfaces.
Different types of fracture:
Uneven/irregular – rough surface
Splintery/fibrous – looks like broken wood
Concoidal - curved surfaces

7. Physical Properties of Minerals (cont.)
Hardness
The measure of the ability of a mineral to resist scratching is called hardness.
Hardness does not mean resistance to cleavage or fracture.
To determine hardness of an unknown mineral, it is scratched against those on the Mohs hardness scale.
The scale lists 10 minerals in order of increasing hardness.
The strength of the bonds between the atoms that make up a mineral’s internal structure determines the hardness of that mineral

8. Physical Properties of Minerals (cont.)
Crystal Shape
A mineral crystal forms in one of six basic shapes.
A certain mineral always has the same general shape because the atoms that form the mineral’s crystals always combine in the same geometric pattern.
The six basic shapes can become more complex as a result of environmental conditions, such as temperature and pressure during crystal growth.

9. Physical Properties of Minerals (cont.)
Density
Density is the ratio of the mass of a substance to the volume of the substance.
Some minerals may feel heavier than others even though they are equal-sized.
The density of a mineral depends on the kinds of atoms that the mineral has and depends on how closely the atoms are packed.

10. 7. Special Properties of Minerals
All minerals exhibit the properties that were described earlier, but a few have some additional, special properties.
Fluorescence and Phosphorescence
The ability to glow under ultraviolet light is called fluorescence.
Fluorescent minerals absorb ultraviolet light and then produce visible light of various colors.
Phosphorescence is when the mineral continues to glow after the ultraviolet light is turned off.

11. Special Properties of Minerals (cont.)
Chatoyancy and Asterism
In reflected light, some minerals display a silky appearance that is called chatoyancy.
Also called the cat’s-eye effect.
A similar effect called asterism is the phenomenon in which a six-sided star shape appears when a mineral reflects light.
Double Refraction
Bending of light rays as they pass from one substance to another is called refraction.
Some transparent minerals bend light in such a way that they produce a double image of any object viewed through them, called double refraction.

12. Special Properties of Minerals (cont.)
Magnetism