MINERALSMINERALS

• What is a mineral? • How do we differentiate a mineral

from a piece of wood or a human? • What is a rock?

Minerals• What is a mineral?

Naturally occurring (not man-made)

Inorganic Crystalline Solid (interlocked

pattern of molecules) Definite chemical structure which

give it unique physical properties.

Ex. Diamonds

Minerals vs. Rocks

• There are nearly 4000 known minerals - but most rocks are formed by only a few dozen minerals.

• Rocks are aggregates (mixtures) of minerals. So . . . minerals are the building blocks of rocks.

• Question :

How do minerals come together to form a rock?

Composition and Structure of Minerals

• To understand how minerals form, we need to understand the characteristics of elements and atoms. Elements are the basic building

blocks of minerals. There are over 100 known elements.

Atoms are the smallest particle of matter that exhibits all the characteristics of an element.

Composition and Structure of Minerals

Atoms are made up of: Nucleus, which contains

Protons- positive electrical charges Neutrons - no charge

Shells which surround the nucleus and contain Electrons - negative electrical charges

• The mass (density) of an element depends on the number of protons and neutrons in the nucleus.

Combining Elements to Form Minerals

Elements combine with each other to form a wide variety of minerals.

The new mineral (compound) will have very different physical properties from the elements that combined to form it.

Ex: 1 Calcium

1 Carbon CaCO3

3 Oxygen

Combining Elements to Form Minerals

Since rocks are mixtures (not chemical combinations) of minerals, minerals keep their physical properties within a rock.

Question: Is it possible for two different minerals to have the same chemical composition?

YES! Both diamond and graphite are made of carbon. The difference between these two minerals is the way in which the carbon atoms are arranged.

Rock Forming Minerals• The most common rock forming

minerals are composed of 8 elements: Oxygen (O) Silicon (Si) Aluminum (Al) Calcium (Ca) Sodium (Na) Potassium (K) Iron (Fe) and Magnesium (Mg)

• There are just a few dozen minerals that we call the rock-forming minerals.

Silicate Minerals• Silicate minerals:

Contain both silicon (Si) and oxygen (O) The most common rock-forming minerals May contain one or more other elements

• Silicates make up 96% of the Earth’s crust.

Silicate Mineral Groups• Feldspars – form depending on which

metal combines with the Si + O atoms Two common types of feldspars:

Orthoclase (K, Al) Plagioclase (Ca, Na)

Most plentiful mineral group

• Quartz – composed ONLY of Si + O atoms

( NO other elements )

Silicate Minerals

Non-Silicate Minerals• Major groups: *Contain no Silicon

Oxides (metal + O) Ex. Hematite, magnetite Sulfides (metal + S) Ex. Pyrite “fool’s gold,”

galena Sulfates (S +O) Ex. Gypsum [plaster] Halides Ex. Halites [salt] "Native" elements (don’t combine with any

other elements) Ex. Gold, silver, carbon, copper Carbonates (C + O) Ex. limestone, marble

Non-Silicates make up 4% of the Earth’s crust.

Non-Silicate Minerals

Non-Silicate Minerals

Mineral Properties• Minerals have lots of different properties

that help us identify them: Crystal form -set of faces that have a definite

geometric relationship to one another. Luster –metallic or nonmetallic shine Color Streak –mineral’s color in powdered form Hardness –Mohs hardness scale/scratch

resistance of one mineral against another Cleavage –how it breaks along preferred

planes Fracture –no preferred plane (no flat surface) Specific gravity -describes the density of the

mineral Taste, Smell, Fluorescence etc.

Identifying Minerals

• Color – can help with mineral identification.

• Color of the mineral• Color of the streak on

a porcelain plate• Example = Hematite is

gray in color and has a red streak

Identifying Minerals

• Luster – shiny or dull• Luster - the way a

mineral reflects light • Look for luster on a

fresh surface. • The three major types of

luster are metallic, glassy (vitreous) and dull.

Plane Name

1 =Basal

2

3

3

=Prismatic

=Cubic

=Rhombo-hedral

Cleavage – how mineral breaks

(a) cubic (b) 12-sided (c) octahedral (d) hexagonal

Identifying Minerals• Most minerals (except metals) have one or more

cleavage planes that also help in determining their identity.

• Cleavage Plane – A region where a rock cleanly splits

• Occur in areas of weak bonds between atoms and molecules.

• Mica has 1 cleavage plane • Halite has 3 cleavage planes

Mohs hardness scaleMohs hardness scale1. Talc 7. Quartz2. Gypsum/fingernail 8. Topaz3. Calcite/penny 9.

Corundum4. Fluorite 10.

Diamond5. Apatite6. Potassium Feldspar/steel nail

Scratch one mineral against another to see how resistant it is.

MaterialMaterial Mohs hardness scaleMohs hardness scale

Streak plate ~7

Glass plate 5.5 - 6

Nail ~4

Copper/Penny ~3

Fingernail ~2

Mineral Identification

• Common items to test for hardness

• A fingernail (2.5) will scratch gypsum and be scratched by calcite

• A penny (3) is scratched by fluorite

• Glass (5.5- 6) scratches apatite and is scratched by orthoclase (a feldspar)