Minerals: Building blocks of rocks

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?


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


Introduction

Minerals exhibit the following characteristics:

• naturally occuring

• inorganic

• solid

• definite chemical structure

Definitions


Introduction Properties of minerals

Major properties of minerals:

• crystal form

• luster

• color

• streak

• hardness

• cleavage

• fracture

• specific gravity



Crystal form – external arrangement of the orderly internal arrangement of atoms


A supersaturated solution readily forms crystals

Crystallization occurs when the KE of individual molecules decreases.


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



Luster – appearance or quality of light reflected from the surface



Luster

• metallic luster

• submetallic luster

• nonmetallic luster

• vitreous

• pearly

• silky

• resinous

• earthy



Color – very unreliable diagnostic property due to impurities



Streak

• color of a mineral in its powdered form

• use a streak plate

• more reliable than color

• metallic (dense, dark streak) vs. nonmetallic





Hardness

• resistance of a mineral to abrasion or scratching

• use the Mohs scale



Cleavage

• a mineral will break along weak bonds when stressed

• tendency of a mineral to break along planes of weak bonding

• 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



Some examples of cleavage



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



Some examples of fracture

Fibrous fracture – note formation of parallel fibers Conchoidal fracture

– note smooth curved surfaces



Specific gravity - compares the weight of a mineral to the weight of an equivalent volume of water


Introduction Mineral groups

Mineral groups

Silicates

• most common

• made of oxygen and silicon

• silicon-oxygen tetrahedron is the fundamental building block



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





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



Dark silicate minerals

• ferromagnesian silicates

• contains iron and/or magnesium

• dark color and greater specific gravity



olivine

hornblende biotite



Light silicate minerals

• nonferromagnesian silicates

• contains Al, K, Ca, and/or Na

• light color and smaller specific gravity



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



rose quartz

plagioclase feldspar

orthoclase feldspar



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)



limestone



pink halite

gypsum



malachite





Minerals: Building blocks of rocks

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Minerals: Building blocks of rocks