MINERALS. Minerals must have four characteristics: ▪ it must be inorganic—not made of or by...

MINERALS

What is a Mineral?

Minerals must have four characteristics:▪ it must be inorganic—not made of or by

living things;▪ it must occur naturally—it cannot be man-

made;▪ it must be a crystalline solid;▪ it must have a consistent chemical

composition.

Types of Minerals

10 are so common that they make up 90% of Earth’s crust. quartz, orthoclase, plagioclase, muscovite,

biotite, calcite, dolomite, halite, gypsum, and ferromagnesian minerals.

Two main groups: silicate minerals nonsilicate minerals

Silicate Minerals

Contain silicon and oxygen, and possibly one or more metals

Common silicate minerals quartz, feldspars, micas ,and ferromagnesian

minerals, such as amphiboles, pyroxenes, and olivines.

Make up 96% of Earth’s crust. Quartz and feldspar alone make up more than

50% of the crust.

Nonsilicate Minerals

No silicon and oxygen compounds

Make up about 4% of Earth’s crust.

Six major groups based on their chemical compositions carbonates, halides, native elements,

oxides, sulfates, and sulfides.

Mineral Structure

Each type of mineral is characterized by a specific geometric arrangement of atoms, or its crystalline structure.

A crystal is a solid whose atoms, ions, or molecules are arranged in a regular, repeating pattern

Silicate Structure

Silicon-Oxygen Tetrahedron- basic unit of the structure of silicate minerals. Si+4 and 4 O-2

Ex: Olivine

Ex: Beryl and tourmaline

Silicate Structure

Ex: Pyroxenes

Ex: Amphiboles

Silicate Structure

Ex: Biotite and muscovite

Silicate Structure

Ex: Quartz and feldspar

Nonsilicate Structure

Diverse chemical compositions = vast variety of crystalline structures.

Common nonsilicate mineral structures: cubes, hexagonal prisms, and irregular

masses.

Mineral Identification

Mineralogist- a person who examines, analyzes, and classifies minerals

Chemical composition and crystalline structure determine a minerals properties

Many of these properties can be used to identify a mineral sample.

Mineral Properties

ColorEasily observed but unreliable

for mineral identification.Can be affected by impurities or

weathering.

StreakColor of a mineral in powdered

formStreak is more reliable than color

for the identification of minerals.

Mineral Properties

Luster

The way a mineral reflects light

Metallic luster- reflects light like polished

metals.

Nonmetallic luster- duller appearance

glassy, waxy, pearly, brilliant, and earthy.

Mineral Properties

Mineral Properties

Cleavage- tendency of a mineral to split along specific planes to form smooth, flat surfaces

Cleavage and Fracture

Mineral Properties

Types of Cleavage Muscovite Halite

Feldspar

Mineral Properties

Fracture- breaks along curved or irregular surfaces Uneven or irregular

fractures Splintery or fibrous

fractures Conchoidal

fractures

Cleavage and Fracture

Mineral Properties

Hardness

Ability of minerals to resist scratching.

Does NOT mean “resistance to cleavage or fracture.”

Determined by comparing to minerals

Mohs hardness scale the standard scale for the

hardness of minerals.

The strength of the bonds between the atoms of a

mineral determines its hardness.

Mineral Properties

Mineral Properties

Crystal Shape

Certain minerals always have the same general shape because the atoms that form the mineral’s crystals always combine in the same geometric pattern.

The six basic crystal systems: isometric or cubic, orthorhombic, tetragonal,

hexagonal, monoclinic, and triclinic

Mineral Properties

Mineral Properties

Density

density the ratio of the mass of a substance to the volume of a substance

The density of a mineral depends on the kinds of atoms in the mineral and on how closely the atoms are packed.

density = mass volume

Special Properties of Minerals

The ability to glow under UV light is called fluorescence.

The property of some minerals to glow after the ultraviolet light is turned off is called phosphorescence.

Fluorescence and Phosphorescence

Chatoyancy and Asterism

Light is reflected causing a silky appearance that is called chatoyancy Tiger’s Eye

A similar light reflecting effect called asterism is when a six-sided star appears Star Sapphire

Special Properties of Minerals

Double Refraction

Producing a double image of objects viewed through the mineral.

Special Properties of Minerals

MagnetismAre attracted to

magnets or may be magnetic themselves.

In general, nonsilicate minerals that contain iron are more likely to be magnetic than silicate minerals are.

Special Properties of Minerals

Radioactivity

The property known as radioactivity results as unstable nuclei decay over time into stable nuclei by releasing particles and energy.

A Geiger counter is used to detect the released particles and, thus, to identify minerals that are radioactive.

Special Properties of Minerals

Value of Minerals