Ch. 5 Minerals - Welcome to Miss Loulousis'...
Transcript of Ch. 5 Minerals - Welcome to Miss Loulousis'...
CH. 5 MINERALS
Loulousis
Objectives 5.1
Define the term mineral
Identify the 2 ways that minerals form
Compare the two main groups of minerals
Mineral Song
http://www.youtube.com/watch?v=-F0IA21bgmM
An Introduction
Mineralogy- study of minerals, subdivision of geology
96% of Earth’s crust is composed of minerals
Atoms make up minerals, minerals make up rocks
How Minerals Form
Crystallization: process of mineral formation, atoms are arranged to form material with crystal structure
1. Solidification of a melt
Magma or lava cools and hardens
How most rocks form
2. Precipitation from solution
Liquids cool to solid state
Precipitation from solution
Example: Salt water
Contains electrically charged atoms (ions)
When salt water evaporates the water becomes saltier, because the ions left behind which are attracted to each other and begin to link together and form mineral crystals
Any natural water will precipitate some minerals through evaporation
Mineral Characteristics Mineral: a natural, inorganic solid that has a
characteristic chemical composition, an orderly internal structure, and a characteristic set of physical properties.
To be a mineral, a substance must have four characteristics:
it must be inorganic—it cannot be made of or by living things;
it must occur naturally—it cannot be man-made; it must be a crystalline solid; it must have a consistent chemical composition.
1. Inorganic
Inorganic- when substance is not made of living things or the remains of living things
Minerals are not organic compounds unlike amino acids, peptides or enzymes are
Oddly, many organic processes result in the formation of minerals ex) teeth and bones
2. Naturally Occurring
Found and created in nature
Products of industrial or commercial processes are not true minerals
3. Solid crystalline structures
Crystalline means that atoms within the solid are arranged in a geometric pattern
The pattern is unique to each mineral
If pattern is altered, it creates a new mineral
Ice is a mineral, while liquid water and steam is not
4. Chemical composition
All minerals have a chemical composition
Means there is a chemical formula for each mineral ex) NaCl
There are some impurities in minerals which means an element may slip into a crystalline structure that should not be there
Four Characteristics of Minerals
Mineral yes or no ? http://www.oum.ox.ac.uk/thezone/minerals/define/quiz/
Kinds of Minerals
More than 3,000 kinds of minerals, but only about 20 are common
Common minerals are rock-forming minerals
10 common minerals make up 90% of the mass of Earth’s crust
Quarts, orthoclase, plagioclase, muscocvite, biotite, calcite, dolomite, halite, gypsum, and ferromagnesian
1. Silicate Minerals
Mineral that contains a combination of silicon and oxygen
Can have one or more metals in addition to silicate and oxygen
Feldspars are the most common
Silicate minerals make up 96% of the Earth’s crust
2. Nonsilicate Minerals
Mineral that does not contain compounds of silicon and oxygen
About 4% of Earth’s crust
6 major : carbonates, halides, native elements, oxides, sulfates, sulfides
Exit Slip
1. What are the two ways minerals form?
2. What are the 4 characteristics of a mineral?
3. What are silicate minerals?
4. What are non-silicate minerals?
Objectives
Identify and describe the 6 types of silicate crystalline structures
Describe three common nonsilicate crystalline structures
Crystalline Structure
Each type of mineral is characterized by a specific geometric arrangement of atoms
Crystal: a solid whose atoms, ions, or molecules are arranged in a regular repeating pattern.
Scientists determine the structure of crystal by using X rays
There are 6 basic crystal shapes
Crystalline Structure of Silicate Minerals Silicate minerals all have the same basic
building blocks of silicon-oxygen tetrahedra that forms its crystalline structure
silicon-oxygen tetrahedron : basic unit of the structure of silicate minerals; a silicon ion chemically bonded to and surrounded by four oxygen ions
* you should be familiar with images of all the silicate mineral structures! Pg. 107
1. Isolated Tetrahedral
Do not link with other silicon or oxygen atoms
Only atoms other than silicon and oxygen atoms link with the silicon-oxygen tetrahedra
Example: olivine, oxygen from tetrahedra links with Mg or Fe atoms
2. Ring silicates
Form rings by sharing oxygen atoms
Can form three, four, or six sided rings that align to make channels for ions or molecules
Ionic bonds hold the rings together
Example: Beryl and Tourmaline
3. Single-Chain Silicates
Form a chain by sharing oxygen atoms
Each tetrahedron is bonded to two others by shared oxygen atoms
Called pyroxenes
4. Double-Chain Silicates
Form when two single-chains of tetrahedra bond to each other
Called amphiboles
5. Sheet Silicates
Form when each tetrahedron shares three of its oxygen atoms with other tetrahedra
The fourth oxygen atom bonds with an atom of Al or Mg which connects the sheets together
Examples: muscovite and biotite
6. Framework silicates
Form when each tetrahedron is bonded to four other tetrahedra
Frameworks that contain only silicon-oxygen tetrahedra form the mineral quartz
Feldspars contain tetrahedra with Al or other metals in place of the silicon
Crystalline Structure of Nonsilicate Minerals Common crystal structures include cubes,
hexagonal prisms, and irregular masses Can form tetahedral similar to silicates but the
ions at the center are not silicon The structure of a nonsilicate crystal
determines the mineral’s characteristics.
In crystal structure called closest packing, each metal atom is surrounded by 8 to 12 other metal atoms that are as close to each other as the charges of the atomic nuclei allow.
Stop and Think
1. What compound of elements will you never find in a nonsilicate mineral?
2. What is the building block of the silicate crystalline structure?
Objectives
Describe the seven physical properties that help distinguish one mineral from another
List the 5 special properties that may help identify certain minerals
Identify minerals using their seven physical properties
5.2 Identifying Minerals
To identify minerals scientists called mineralogists examine and analyze the properties of minerals
Each mineral has specific properties that are a result of its chemical composition and crystalline structure
1. Color
color is a property that is easily observed, but by itself is unreliable for the identification of minerals.
The color of a mineral sample can be
affected by the inclusion of impurities or by weathering processes.
2. Streak
Streak: color of a mineral in powdered form
Observed by rubbing some of the mineral on an unglazed ceramic tile called a streak plate
Streak color can differ from the color of the solid mineral
Streak is more reliable than color for the identification of minerals
3. Luster
Luster: the way in which a mineral reflects light A mineral is said to have a metallic luster if the
mineral reflects light as a polished metal does.
All other minerals have nonmetallic luster.
There are several types of nonmetallic luster, including glassy, waxy, pearly, brilliant, and earthy.
Mini video
4. Hardness
Hardness: the measure of the ability of a mineral to resist scratching
Hardness does not mean “resistance to cleavage or fracture.”
The hardness of a mineral can be determined by comparing the mineral to minerals of Mohs hardness scale.
Mohs hardness scale: the standard scale against which the hardness of minerals is rated
The strength of the bonds between the atoms that make up a mineral’s internal structure determines the hardness of a mineral.
Mohs Hardness Scale
5. Cleavage and Fracture
Cleavage: in geology, the tendency of a mineral to split along specific planes of weakness to form smooth, flat surfaces
Fracture: the manner in which a mineral breaks along either curved or irregular surfaces
Uneven or irregular fractures have rough surfaces.
Splintery or fibrous fractures look like a piece of broken wood.
Curved surfaces are conchoidal fractures . Mini video
6. Crystal shape
6 basic chapes: isometric or cubic, tetragonal, monoclinic, orthorhombic, hexagonal, triclinic
A certain mineral always has the same general shape because the atoms that form the mineral’s crystals always combine in the same geometric pattern
Review table 2 on pg. 112
7. Density
Density: the ratio of the mass of a substance to the volume of a substance; commonly expressed as grams per cubic centimeter for solids
The density of a mineral depends on the kinds of atoms in the mineral and on how closely the atoms are packed.
density = mass volume
8.Special Property: Fluorescence and Phosphorescence
Fluorescence: The ability to glow under ultraviolet light
Fluorescent minerals absorb ultraviolet light and then produce visible light of various colors.
Phosphorescence: The property of some
minerals to glow after the ultraviolet light is turned off
9.Special Property: Chatoyancy and Asterism In reflected light, some minerals display a
silky appearance that is called chatoyancy, or the cat’s-eye effect.
A similar effect called asterism is the phenomenon in which a six-sided star appears when a mineral reflects light.
Double refraction: The property of some minerals to produce a double image of any object viewed through the mineral Example: calcite
Magnetism
Minerals that are attracted to magnets display the property of magnetism.
These minerals may be magnetic
themselves.
In general, nonsilicate minerals that contain iron are more likely to be magnetic than silicate minerals are.
Radioactivity
Radioactivity results as unstable nuclei
decay over time into stable nuclei by releasing particles and energy.
A Geiger counter is used to detect the released particles and, thus, to identify minerals that are radioactive.
Stop and Think
What determines the hardness of a mineral?
What is the difference between chatoyancy and asterism?
What is the two main types of luster?