Unit 2Chapter 5

Minerals of Earth's Crust

Minerals:

Are naturally occurring, inorganic solid that has a definite chemical composition with the atoms arranged in an orderly pattern.

Characteristics of Minerals There are 4 characteristics that the object must

fit into• Is it organic?• Does it occur naturally?• Is it a crystalline solid?• Does it have a definite chemical composition?

Kinds of Minerals

There are approximately 4000 known minerals

Approximately 20 of the minerals are called rock forming and approximately 90% makes up the earth's crust. 90% of the minerals are a combination of the common elements. The rest of the minerals are rare or in rare quantities.

Silicate Minerals Silicate

A mineral that contains a combination of silicon and oxygen.Most common minerals that make up approx 95% of the earth's crustCommon ones include: quartz and the feldspars

(rocksandminerals4u) Non Silicate Minerals

Carbonates Contain carbon

Halides

Chlorine, fluorine combined with sodium, potassium or calcium Native Elements

Composed of a single elementGold - AuSilver - AgSulfur - SDiamond - C

OxidesContain Oxygen and other elements

SulfatesContain sulfate (SO4) and other elements

SulfidesContain Sulfur and other elements

Crystalline Structure

Crystal:Atoms that are arranged in a regular repeating pattern.Can be seen with your eye, microscope or x-ray

Crystalline Structure of Silicate Minerals

Silicon-Oxygen Tetrahedron Basic building block of rocks in the earth's crust4 Oxygen

1 Silicon

Hint - know this name and this shape it may come up again!!!!

Hornblende - Silicon Tetrahedrons form the shape of a chain. - Oxygen will bond with Si to form a bumpy thing

Mica - Si tetrahedrons form a flat sheet Pyroxene- Si tetrahedrons form a chain

Section 2 Identifying Minerals

MineralogyThe study of minerals

Mineralogist

The scientist who studies minerals

Physical properties of Minerals:

Color -Easy to determine but not too good because many minerals have the same color Also many minerals may have more than one color.

Reasons: 1. impurities may change color2. Air may change color3. Many different minerals may have the same color

Streak Test

By using an unglazed white tile and rubbing the mineral over the tile it can produce a powder. Each mineral's streak is always the same color no matter what the color of the mineral is.

Luster Metallic - looks and shines like a metal

Non metallic - can be shiny but does not look like a metal

Cleavage and Fracture Cleavage

The tendency of a mineral to split easily or separate along flat surfaces.Ex. Mica - one directional perfect cleavage

Fracture -

The mineral breaks along a surface that is not a cleavage surface.

1c. Conchoidal -shell like fracture Ex. Obsidian

2c. Fibrous - splintery - produces jagged, sharp edges Ex. Copper

3c. Uneven or irregular - generally rough surfaces

Hardness -It is the resistance to being scratched. If a mineral scratches another mineral it is harder than the other mineral.

Moh's Hardness Scale

Uses objects easily found with earlier geologists.

1. Finger Nails2. Copper penny (prior to ~1975)3. Steel (knife)4. Glass (watch or glasses)

The scale

Mohs (mineralogist, 1773-1839) scale is used mostly. Rosiwal shows cutting strength and Vickers shows denting strength.

CrystalIt is a shape only easily observed with large crystals.

Density

Ratio of mass of a substance to the volume of the substance

Density = Mass Volume

Specific Gravity: Simple definition:The objects weight in air verses its weight in water (compares densities)

Special PropertiesFluorescence - the ability to glow under Ultra violet lightPhosphorescence - the ability to glow after lights are turned off

Double Refraction - 2 images can be seen through the mineralEx. Calcite

Magnetism - minerals can be picked up or is attracted to a magnet.Ex. Magnetite

Radioactivity -the ability to release energy and activate a Geiger counterEx. Uranium

Another way to determine a mineral

• Acid Test:• Weak acids can cause calcite to fizz (bubble)

like putting water on an "Alka Seltzer" tablet.