MINERALSA mineral is a naturally occurring, inorganic solid that has a crystal structure and a definite chemical

composition.

HOW MINERALS FORM

Minerals form from Magma * (They form as hot magma cools inside the crust, or as lava

hardens on the surface) *Large crystals form when cooling is slow. *Small crystals form when cooling is fast.Minerals form from a hot water solution.

*Many minerals form at places where tectonic plates spread apart. When the hot solution hits the cool sea, minerals

crystallize and settle to the ocean floor. Minerals form by evaporation *They form when solutions evaporate. *Minerals such as halite formed when ancient seas

evaporated.

CHEMICAL COMPOSITION Minerals are made of atoms.

Some minerals are made of only one kind of atoms, such as gold and silver.

Most minerals are made of two or more kinds of atoms, such as salt. It is made of sodium and chlorine atoms.

Identifying Minerals1. Color -Easily observed but few have characteristic color.2. Hardness -Moh’s hardness scale and scratch test3. Streak -Color of its powder on unglazed tile4. Luster -Term used to describe how a mineral reflects light5. Density -Mass per unit volume6. Crystal systems -Cubic, hexagonal, tetragonal, orthorhombic, monoclinic, triclinic7. –Breakage Cleavage and Fracture8. Special properties (fluorescence, magnetism, scent, react to acid, etc)

ColorDescribing a mineral’s color may be easy,

but color is not the best way to identify a mineral. Sometimes different atoms get trapped inside a mineral when it forms. These different atoms can change the

color of the mineral.

These are all images of halite.

Hardness Hardness is a better way to describe minerals. There is a scale called the Mohs’ hardness scale The low numbers are soft and the higher numbers are hard. Hard minerals can scratch lower numbers The higher a mineral’s number is, the more minerals it can scratch.

The Mohs’ scale is pictured below

1 2 3 4 5

6 7 8 9 10

StreakColor of the powdered form of the mineral

A tool called a streak plate also helps us to study minerals.

A streak plate is made of white tile that can show streak.

Different minerals make lines that are different colors.

Some lines are the color of the mineral and some are not.

Luster

Vitreous SilkyMetallic Earthy

• Luster describes how a mineral appears to reflect light and how brilliant or dull the material is.

• There are terms used to describe luster. They are: adamantine (brilliant), Metallic (very reflective), submetallic, vitreous (glassy), resinous, silky, pearly, greasy (oily), pitchy, waxy (waxlike), earthy (dull).

• 70 % of all minerals fit in the vitreous category.

• This is a test that is based just on visual observations.

Density

This is a useful property to distinguish minerals since they have a specific

density.Pure Gold has a density of 19.3 g/cm3.

Crystal Systems Cubic Crystals

All minerals have a specific crystal system.Cubic crystals are six sides that meet at

right angles, forming a perfect cube

Hexagonal Crystals

One six fold axis of rotationHexagon shaped base

Tetragonal Crystals

One four fold axis of rotation

Orthorhombic Crystals

3 two-fold axis of rotation1 two-fold axis of rotation

2 mirror planes

Monoclinic Crystals

Either one two fold axis of rotationOr one mirror plane

Flat, thin sides

Triclinic Crystals

Requires either a centerOr only translational symmetry

BreakageSome minerals break apart in a special way

due to their atomic arrangement.Cleavage is a term that means the mineral

breaks apart smoothly in flat surfaces.

Fracture is a term that means the mineral breaks apart smoothly in more than one direction.

Special PropertiesFluorescence: some minerals have afluorescent glow under black light.

Magnetism: some minerals have Magnetic force.

Scent: some mineralshave a distinct odor.

Reacts to Acid: some minerals have aReaction to acids.

Mineral Value

Many minerals are very expensive and highly valued.

How rare a mineral is determines its value.

Minerals can be enhanced by dying, oiling, polishing and cutting.