GEOL 101 Ch 3 - Minerals

What is a mineral

A naturally occurring inorganic solid with a specific chemical composition and an orderly internal arrangement of atoms

What is a rock

A naturally occurring aggregate or mass of minerals, crystals, grains, fragments, or glass

What is the main difference between a mineral and a rock

A mineral has a specific composition and crystal structure; a rock is an aggregate of materials/minerals

What are the three main parts/particles of an atom

Protons, neutrons, and electrons

What charge does a proton have

Positive (+)

What charge does a neutron have

No charge

What charge does an electron have

Negative (−)

Where are protons and neutrons found

In the nucleus

Why are electrons important in mineral formation

They control how atoms bond with one another

What are the three major types of atomic bonding in this chapter

Ionic, covalent, and metallic bonding

What happens in ionic bonding

Electrons are gained or lost, forming oppositely charged ions that attract each other

What mineral is the main example of ionic bonding

Halite, NaCl

What happens to sodium and chlorine in NaCl

Sodium loses an electron and becomes Na⁺; chlorine gains it and becomes Cl⁻

What happens in covalent bonding

Atoms share electrons

What mineral is the main example of covalent bonding

Diamond

What happens in metallic bonding

Electrons move relatively freely from one atom to another

Examples of metallic bonding

Native copper, silver, and gold

What is crystal structure

The orderly arrangement of atoms or ions into repeated three-dimensional units

Why can minerals have characteristic crystal shapes

Their external form reflects their internal atomic arrangement

What is a crystal

A single, continuous piece of a mineral that grew to its present form

What is a euhedral crystal

A crystal that grew in open space and developed smooth, well-formed crystal faces

What is an anhedral crystal

A crystal that grew in a confined space and lacks distinct crystal faces

Does an anhedral crystal have a disordered internal structure

No

Its exterior may be irregular, but its atoms are still orderly arranged

What is a crystal face

A smooth, flat external surface formed during crystal growth

How can X-rays be used to study crystals

X-rays diffract through a crystal and produce a pattern that reveals the atomic arrangement

What causes the bright spots in an X-ray diffraction pattern

Constructive interference of diffracted X-rays

What is a mineral group

Minerals that share the same general crystal structure but differ slightly in chemical composition

What are polymorphs

Minerals with the same chemical composition but different crystal structures

Classic example of polymorphs

Diamond and graphite

Why are diamond and graphite so different if both are carbon

Their carbon atoms have different crystal structures and bonding arrangements

What processes can destroy or transform minerals

Melting, dissolution, chemical reactions, phase changes, and microbial activity

Why does melting destroy a mineral

It destroys the organized crystal structure, even though the atoms remain

What is color in a mineral

The visible wavelengths of light that the mineral does not absorb

Why is color often unreliable for mineral identification

The same mineral may occur in several colors

What is streak

The color of a mineral’s powder

How is streak tested

By scraping the mineral on an unglazed porcelain plate

Why is streak usually more reliable than color

Streak is more consistent than the external color of a mineral specimen

What is luster

The way a mineral’s surface scatters or reflects light

What are the two broad luster categories

Metallic and nonmetallic

What are examples of nonmetallic luster

Vitreous, satiny, pearly, and earthy

What does vitreous mean

Glassy

What is specific gravity

The ratio of the weight of a mineral to the weight of an equal volume of water at 4°C

What does a high specific gravity mean

The mineral feels relatively heavy for its volume

What is crystal habit

The characteristic shape of a crystal or aggregate of crystals as it grows

What mainly controls crystal habit

The internal arrangement of atoms

What is hardness

A mineral’s resistance to scratching

What does hardness reflect

The strength of bonds in the crystal structure

What scale is used to compare mineral hardness

The Mohs hardness scale

If Mineral A scratches Mineral B, which is harder

Mineral A

What is cleavage

The tendency of a mineral to break along flat, planar surfaces

Why does cleavage occur

Atomic bonds are weaker in certain directions in the crystal structure

What two things are important when describing cleavage

The number of cleavage planes and the angles between them

What is the difference between a cleavage plane and a crystal face

A cleavage plane forms when a mineral breaks; a crystal face forms during crystal growth

Which can repeat throughout the interior: cleavage planes or crystal faces

Cleavage planes

What visual clue may indicate cleavage

Repeated flat surfaces or tiny steps

What is fracture

Breakage that does not occur along flat cleavage planes

What is an example of fracture

Conchoidal fracture

Other useful mineral properties

Effervescence, taste, smell, magnetism, striations, etc

What is a gemstone

A mineral with special economic value because of beauty and rarity

What can “rarity” mean for a gemstone

The gem-quality form may be rare even if the mineral itself is common

What is the most common mineral group on Earth

Silicates

What structural unit do silicates contain

The silicon-oxygen tetrahedron, SiO₄

Examples of silicate minerals

Quartz, mica, feldspar, hornblende, augite, and olivine

What do carbonates contain

The carbonate ion, CO₃

Examples of carbonates

Calcite and dolomite

What important behavior do carbonates have

They dissolve readily in acidic water

What are halides

Minerals formed when positive ions combine with negative halogen ions such as Cl or F

Examples of halides

Halite, sylvite, and fluorite

What are oxides

Minerals formed when oxygen combines with positive metallic ions

Examples of oxides

Hematite and magnetite

What are sulfides

Minerals in which sulfur combines with a positive ion, usually a metal

Examples of sulfides

Galena, pyrite, and chalcopyrite

What are sulfates

Minerals containing the sulfate ion, SO₄

Examples of sulfates

Gypsum, anhydrite, and barite

Sulfide vs

sulfate

Sulfides contain sulfur; sulfates contain the SO₄ complex ion

What are native elements

Minerals consisting of a single element

Examples of native elements

Gold, silver, platinum, copper, diamond, graphite, and sulfur

What are the three major rock categories

Igneous, sedimentary, and metamorphic

How do igneous rocks form

By solidification of molten rock or by binding erupted volcanic fragments

How do sedimentary rocks form

By cementation of loose clasts, shells, or precipitated material

How do metamorphic rocks form

By transformation of pre-existing rock without melting

If a rock melts and then solidifies, what type of rock forms

Igneous

What are three general rock textures mentioned in the chapter

Crystalline, clastic, and glassy

What characteristics do geologists use to describe rocks

Composition, grain size, grain shape, texture, fabric, and layering