Minerals:

Building blocks of rocks

Minerals: Building blocks of rocks

Introduction

• What are minerals and how are they different from rocks?

• What are some of the physical and chemical properties of minerals?

• What is the most abundant mineral group? What do all minerals in this group have in common?

• What are some important nonsilicate minerals?

• When is the term ore used with reference to a mineral?

Minerals: Building blocks of rocks

Introduction Definitions

Minerals versus rocks• rock – an aggregate of minerals

• aggregate – minerals occur together as a mixture

• each mineral retains its distinctive properties

• mineral – a naturally occurring inorganic solid that possesses a definite chemical structure, which gives it a unique set of physical properties

Minerals: Building blocks of rocks

Introduction

Minerals exhibit the following characteristics:• naturally occuring• inorganic• solid• definite chemical structure• unique set of physical properties

Definitions

Minerals: Building blocks of rocks

Introduction Properties of minerals

Major properties of minerals:• crystal form• luster• color• streak

• hardness• cleavage• fracture• specific gravity

Minerals: Building blocks of rocks

Introduction Properties of minerals

Crystal form

external arrangement of the orderly internal arrangement of atoms

Minerals: Building blocks of rocks

A supersaturated solution readily forms crystals

Crystallization occurs when the KE of individual molecules decreases.

Introduction Properties of minerals

Crystal form – clearly evident only when the mineral forms without space restrictions

Crystals form as they overcome solvation forces

Most minerals form under intense competition for space

Minerals: Building blocks of rocks

Introduction Properties of minerals

Minerals: Building blocks of rocks

Introduction Properties of minerals

Luster

appearance or quality of light reflected from the surface

Minerals: Building blocks of rocks

Introduction Properties of minerals

Luster• metallic luster• submetallic luster• nonmetallic luster• vitreous• pearly• silky• resinous• earthy

Minerals: Building blocks of rocks

Introduction Properties of minerals

Color

Very unreliable diagnostic property due to impurities

Wavelength of visible light bouncing off a surface

Minerals: Building blocks of rocks

Introduction Properties of minerals

Streak• color of mineral powder• streak plate• more reliable than color• metallic (dense, dark streak) vs. nonmetallic

Minerals: Building blocks of rocks

Introduction Properties of minerals

Minerals: Building blocks of rocks

Introduction Properties of minerals

Hardness

resistance of a mineral to abrasion or scratching

use the Mohs scale

Minerals: Building blocks of rocks

Introduction Properties of minerals

Cleavage• tendency of a mineral to break along planes of

weak bonding when stressed• cleavage is described by the number of planes

formed and the angles in which these planes meet

• not all minerals have definite planes of cleavage

Minerals: Building blocks of rocks

Introduction Properties of minerals

Some examples of cleavage

Minerals: Building blocks of rocks

Introduction Properties of minerals

Fracture• minerals that do not exhibit cleavage tend to

fracture when broken• conchoidal fracture – produces smooth curved

surfaces• other types of fracture (splinters or fibers)• most minerals fracture irregularly

Minerals: Building blocks of rocks

Introduction Properties of minerals

Some examples of fracture

Fibrous fracture – note formation of parallel fibers Conchoidal fracture

– note smooth curved surfaces

Minerals: Building blocks of rocks

Introduction Properties of minerals

Specific gravity

compares the weight of a mineral to the weight of an equivalent volume of water

Minerals: Building blocks of rocks

Introduction Mineral groups

Mineral groups

Silicates• most common• made of oxygen and silicon• silicon-oxygen tetrahedron is the fundamental

building block

Minerals: Building blocks of rocks

Introduction Mineral groups

Variants of the silicate structure• addition of metals to stabilize structure (Fe, Mg,

K, Na, Al, and Ca)• sharing of oxygen atoms results to a variety of

configurations• single chains• double chains• sheets

Minerals: Building blocks of rocks

Introduction Mineral groups

Minerals: Building blocks of rocks

Introduction Mineral groups

Variants of the silicate structure• the ratio of oxygen to silicon atoms varies among

the different silicate structures• high or low silicon content based on this ratio• important in the formation of igneous rocks

• families of minerals• same structure but with varying amounts of

metals

• olivine, (Mg,Fe)2SiO4

Minerals: Building blocks of rocks

Introduction Mineral groups

Dark silicate minerals• ferromagnesian silicates• contains iron and/or magnesium• dark color and greater specific gravity

Minerals: Building blocks of rocks

Introduction Mineral groups

olivine

hornblende biotite

Minerals: Building blocks of rocks

Introduction Mineral groups

Light silicate minerals• nonferromagnesian silicates• contains Al, K, Ca, and/or Na • light color and smaller specific gravity

Minerals: Building blocks of rocks

Introduction Mineral groups

Light silicate minerals• feldspars – most common light silicates (most

common mineral on Earth)• orthoclase feldspar – has K ions• plagioclase feldspar – has Na and Ca

• light color and smaller specific gravity• quartz – consists entirely of silicon and oxygen

Minerals: Building blocks of rocks

Introduction Mineral groups

rose quartzplagioclase feldspar

orthoclase feldspar

Minerals: Building blocks of rocks

Introduction Mineral groups

Nonsilicate minerals• carbonate minerals (limestone)• halite (table salt)• gypsum (used in plaster, building materials)• metal ores (Fe, Zn, Pb)• native elements – free occurring, not in compounds

(Au, Ag, C)

Minerals: Building blocks of rocks

Introduction Mineral groups

limestone

Minerals: Building blocks of rocks

Introduction Mineral groups

pink halite

gypsum

Minerals: Building blocks of rocks

Introduction Mineral groups

malachite

Minerals: Building blocks of rocks

Introduction Mineral groups

Minerals: Building blocks of rocks

Introduction Mineral groups