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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 (SO4) 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 xray
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, 1773-1839) 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.