Unit 2 Chapter 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 crust Common 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 element Gold - Au Silver - Ag Sulfur -S Diamond - C Oxides Contain Oxygen and other elements Sulfates Contain sulfate (SO 4 ) and other elements Sulfides Contain 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 crust 4 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 Mineralogy The 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 color 2.Air may change color 3.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 Nails 2.Copper penny (prior to ~1975) 3.Steel (knife) 4.Glass (watch or glasses)

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

Crystal It 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 Properties Fluorescence -the ability to glow under Ultra violet light Phosphorescence -the ability to glow after lights are turned off Double Refraction - 2 images can be seen through the mineral Ex. 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 counter Ex. 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.