Minerals & RocksHonors Notes

A Mineral is a naturally occurring Inorganic Solid with a definite chemical composition and a

crystalline structure.

Lets put that in a list format:1. Minerals are a naturally occurring substance.

2. Minerals are solids. 3. Minerals have a definite chemical composition.4. The atoms that make up minerals are arranged in an orderly pattern (They form crystals).5. Minerals are inorganic. (They were never alive.)

Two Major Types of MineralsSilicate Minerals

◦Contain silicon (Si) plus oxygen (O) or silicon dioxide (SiO2).

◦The most common rock-forming minerals ◦May contain one or more other elements with the silicon

and oxygen. EX: Feldspars are formed depending on what else combines

with the silicon and oxygen.◦Orthoclase- Si, O, K, AL◦Plagioclase- Si, O, Ca, Na

EX: Quartz composed of only Si and O◦Make up 96% of the Earth’s crust.

Earth’s oceanic crust is denser and contains a larger percentage of silicates than continental crust.

Silicate Minerals

Two Major Types of Minerals (cont’d)

Non-silicates◦Contain no silicon◦Many important mineral groups are not silicates.◦Non-Silicate Minerals include: carbonates,

(limestone, marble) oxides (hematite), halides (halite/rock salt), sulfides (pyrite), sulfates (gypsum), and native metals (gold, silver, copper).

◦The non-silicate groups are a source of many valuable ore minerals and building materials.

◦To be an ore, a mineral must occur in large enough quantities to be economically recoverable.

Non-Silicate Minerals

Non-Silicate Minerals

Flourite

Gold

Galena

Physical Properties

Mineral appearance HardnessLusterSpecific gravityStreakCleavage and fracture

Mineral appearance How it looks like What color is it?Which one of the following is gold?

Identify by appearance.

Hardness A measure of how easily a mineral can be

scratched Mohs Hardness Scale

◦ developed in 1812 by Friedrick Mohs (an Austrian mineral expert) as a method to identify minerals.

Luster The way a mineral reflects a light.Either metallic or nonmetallic

Specific GravityThe specific gravity of a mineral is the

ratio of its weight compared with the weight of an equal volume of water.

Gold has specific gravity of 19It means gold is 19 times heavier

than water.

19 times heavier

Specific gravity

Streak When a mineral is rubbed across a piece

of porcelain tile a streak of powdered mineral is left behind.

Cleavage

Cleavage is the way that mineral breaks.

Minerals that break along smooth, flat surfaces have cleavage.

Mica has cleavage

and Fracture!...Mineral that breaks uneven, rough, or

jagged surfaces have fracture.Quartz has fracture

quartz

Atom ArrangementSome physical properties are controlled

by the orderly arrangement of atoms in a mineral’s structure.

The arrangement of atoms and the bonds between them can reflect the way a mineral breaks, how hard it is, and what types of crystal shape it has.

Crystal Shape – Types of Symmetry

Which of these would halite be the shape of?

Plane Name

1 =Basal

2

3

3

=Prismatic

=Cubic

=Rhombo-hedral

An illustration appearance:luster,color and streak

An illustration cleavage and fracture

Identify the minerals below for cleavage and fracture

CLEAVAGE FRACTURE

Special Properties of MineralsMagnetic – use a magnet and see if it sticksTaste – certain minerals have a specific tasteFluorescence – glowing while under a U.V. lightPhosphorescent – continues to glow after the

U.V. light is offRadioactive – test minerals with a Geiger

counterDouble Refraction – Splits light rays into 2

parts. (see a double image) Look through the mineral for the image.

RocksA rock is a naturally formed consolidated

solid mixture made up of minerals, rock fragments, or volcanic glass

Essential Minerals: always occur in the rock

Accessory Minerals: sometimes occur in rock

Classify Rocks by how they formIgneous

◦ - Made up of magma or lava when it cools and hardens

Sedimentary◦ - Made from sediments

Metamorphic◦ - Rocks changed by pressure &

heat

Igneous RocksFormed from lava or magma

◦Lava : extrusive or volcanic◦Magma: Intrusive or plutonic (pillow-like)

Intrusive Igneous rocks Formed from magma which cools and solidifies

below Earth’s surface Cooling and solidification take a long time

resulting in large visible crystals (coarse-grained)Extrusive Igneous Rocks

Small to no mineral crystals due to faster cooling lava above Earth’s surface (fine-grained)

Occurs at volcanoes or through ocean floor

Sedimentary Rocks

Rock is a fused mixture of minerals. Some of these minerals could be in bits and pieces of other rocks.

Broken into pieces (clasts) through weathering◦ Rock exposed at the surface is attacked by the weather

Water: enters cracks, expands, & breaks rocks down

Rain: acidic dissolves minerals

Movement in rivers: collects at the bottom

Sedimentary Rocks Formation Build very slowly in layers, until the environment

changes◦ Compaction: pieces compact due to weight squeezing

them together◦ Cementation: minerals acting as cement holding

sediments together◦ Precipitation: water evaporates & minerals are left

behind

Classifying Sedimentary RocksClastic Rocks: pieces of other rocks

NonClastic RocksMinerals in water which evaporates to

leave behind deposits (rocks) or fossil materials that compact into rock.

Ex:◦1. Limestone: calcite and seashells◦2. Rock salt: halite◦3. Rock gypsum: gypsum◦4. Chert: Quartz◦5. Coal: fossil materials

Metamorphic RocksForm from pre-existing igneous,

sedimentary, or metamorphic rocks, as a result of temperature and pressure changes

3 types of changes:1. Rearrangement of mineral grains2. Enlargement of crystals3. Change in chemistry of rock

Characteristics of Metamorphic Rocks Foliation: Foliated textures in metamorphic

rocks have lots of layers or bands.Non-Foliated: metamorphic textures

include rocks whose grains are in more random orientations. (no bands)◦Tend to have random crystal orientation and

uniform grain size.◦Mineral grains tend to grow larger as

metamorphism increases.

Characteristics of Metamorphic Rocks Foliation Nonfoliated

Hints for Identifying RocksIgneous

◦ crystals intersecting at angles◦ size of the grain

Sedimentary◦ layers of rock pieces

Metamorphic◦ pressure created results in lines ◦ pressure and heat create grains in foliation (wavy

patterns)◦ hardest of the 3 rocks

Rock CycleChanges of rocks from one rock type to another

Magma

Igneous Rock

cooling

wea

ther

ing

Sediments cementation or compaction Sedimentary Rock

heat

& p

ress

ure

Metamorphic Rock

melting