GeoFacts•Stalactites and other cave formations made from calcium carbonate take thousands of years to form.•One estimate is that a stalactite will grow only 10 cm every 1000 years.

MINERALS

What is a mineral?

Five characteristics of all minerals:naturally occurringinorganic (was never alive)definite crystal structure (atoms arranged in an

orderly pattern)solidspecific chemical composition (made up of different

elements and compounds)Earth’s crust is composed of about 3000

minerals.

Naturally occurring and inorganic…

Minerals are formed from natural processesAny man-made mineral is called synthetic

Minerals are inorganic because they are not alive and never were aliveSalt is a mineral, but sugar is not. Sugar comes

from plants.Coal is not a mineral because it forms over

thousands of years from the buildup of dead/decaying matter.

Definite crystal structure

The atoms in minerals are arranged in regular geometric patterns that are repeated.

This regular formation is called a crystal

Solids with specific compositions

Solids have definite shapes and volumes; liquids and gases do not.

Many atoms have silicon and oxygen in them, but the arrangement and proportion of elements in these minerals are unique.The formula for quartz is SiO2

The formula for pyroxene is MgSiO3

Common elements found in minerals

Eight elements make up 98.5% of the crust’s total mass:

Name Symbol % by Mass

Oxygen O 46.6

Silicon Si 27.7

Aluminum Al 8.1

Iron Fe 5.0

Calcium Ca 3.6

Sodium Na 2.8

Potassium K 2.6

Magnesium Mg 2.1

More than 90% of the minerals in Earth’s crust are compounds containing OXYGEN AND SILICON, the two most abundant elements.

Most minerals are compounds.Quartz is a compound of silicon and oxygenGalena is a compound of lead and sulfur

A few minerals consist of single elements and are called native elements:Examples: silver, copper, sulfur and diamond

Rock-forming minerals

There are 8 minerals that make up most of the rocks of Earth’s crust.

They are primarily composed of the eight most common elements in Earth’s crust.Quartz, feldspar, mica, pyroxeneAmphibole, olivine, garnet, calcite

We’ll talk more about rocks next chapter

Structure of minerals

Identifying minerals

Mineralogy – the study of minerals and their unique properties

Minerals are RARELY identified by one single property

Mineral properties

Color – not the most reliable characteristic; minerals change color with a change in temperature, pressure or metal

Mineral properties

Luster – describes how minerals shine in natural light We classify minerals as having metallic or non-metallic

luster. Not all metallic minerals are metals!! We further classify using words such as vitreous, pearly,

greasy, oily, dull, earthy

Mineral properties

Streak – the color of a mineral’s powder; in many cases the streak will not be the same color as the mineral.The streaks of nonmetallic minerals are usually colorless

or white

Mineral properties

Hardness – resistance to being scratchedDiamond is the hardest of all minerals. Talc is the softest of all minerals.

The minerals in the table on the next slide were selected because they are easily recognized and are readily found in nature (except for diamond).

Mohs Scale of HardnessFriedrich Mohs

devised a numeric scale that is used to express the hardness of minerals.

You can determine the approximate hardness of any common mineral by using other common objects

Mineral Hardness Comparison

Talc 1

Gypsum 2 Fingernail = 2.5

Calcite 3 Copper penny = 3.5

Fluorite 4 Iron nail = 4.5

Apatite 5 Glass = 5.5

Feldspar 6 Steel file = 6.5

Quartz 7 Streak plate = 7

Topaz 8

Corundum 9

Diamond 10

Mineral properties

Specific gravity – ratio of a mineral’s mass to the mass of an equal volume of water

It tells you how many more times denser the mineral is than water.

Mineral properties

Texture – the way a mineral feels

This property is very subjective; a mineral may feel different to two people working together

Special properties

HCl chemical test: look for bubbles to formDouble refraction: shows a double imageFluorescence: the ability to glow under UV lightPhosphorescence: the ability to glow in the darkMagnetism: attraction to magnets

Silica Tetrahedron

More than 90% of the minerals in Earth’s crust are silicates.

Silicon and oxygen bond in a way that forms a tetrahedron

Mineral groups

Silicates – quartz and feldspar are the most common minerals found in this groupUses: gems, watches, potting soil additive

Carbonates – calcite and dolomite are the most common mineralsUses: cement for construction, paper, medicines

Mineral groups

Oxide – mineral that has oxygen combined with a metal element; hematite and magnetite are common mineralsUses: abrasives, plumbing fixtures, auto parts

Sulfide – mineral that has sulfur combined with a metal element; pyrite (fool’s gold) and galena are common mineralsUses: jewelry, ores for manufacturing

Mining for minerals

Ores and mines

Ore – minerals that contain useful substances that can be mined for a profit

The classification of a mineral as an ore can also change if the supply of or demand for that mineral changes.

Ores that are located deep within Earth’s crust are removed by mining

Consequence of mining???

Gems

Some minerals are rarer than others and are therefore classified as expensive gems.

Gems – valuable minerals that are prized for their rarity and beauty

Rubies and emeralds are more expensive than diamonds.