Minerals Chp. 30

Mineral = Naturally occurring, inorganic solid with a specific chemical composition and a definite crystalline structure. Normally made of a single element or compound What is a mineral? Compound: atoms of different elements chemically bonded together inorganic Naturally occurring chemical composition definite crystalline structure

Property: Crystal Form Crystal form = External expression of a mineral’s internal orderly arrangement of atoms Pyrite – cubic striations may be present

Quartz - hexagonal Property: Crystal Form

Crystal form = an orderly arrangement of atoms.

How many axis make up each system? How many faces make up each system? Do all the axis meet at 90 degrees? Property: Crystal Form

Variations in crystal form

Property: Hardness Moh’s Hardness Scale= Identifies the hardness of the mineral. The softer material always receives the scratch! Hardness measures the strength of the minerals chemical bonds During scratching bonds between atoms are broken. Diamond10 Corundum9 Topaz8 Quartz7 Orthoclase (Feldspar)6 Apatite5 Fluorite4 Calcite3 Gypsum2 Talc1 Fingernail 2.5 Copper penny3 Glass5.5 Nail6.5

Property: Cleavage Cleavage = Tendency of a mineral to break along planes of weakest chemical bonds. –Not all minerals have definite planes of weak bonding.

Basal = one plane –Micas Biotite Muscovite Property: Cleavage

Property: Fracture Fracture = a break that is not along a cleavage plane Conchoidal fracture = Smooth, curved and resembles broken glass..

2. Luster Luster = Appearance or quality of light reflected from the surface of a mineral. a)Metallic luster = the appearance of metal Pyrite – FeS 2 Copper - Cu

2. Luster b.Nonmetallic luster i.Vitreous – glassy

3. Color Obvious feature, but unreliable.

4. Streak Streak = Color of a mineral in its powdered form. hematite – red brown

Specific Gravity Specific Gravity = Compares the weight of a mineral to the weight of an equal volume of water

Other Properties Halite – salty = Taste Magnetite – magnetic = magnetism Calcite – effervesces = Acid test/effervescence

What are minerals, how are they formed? Element: fundamental material consisting of only one type of atom Compound: atoms of different elements chemically held together Atom of Lithium (3 P + )

How are minerals formed? 1.From magma 2.Precipitation 3.Temp/Pressure changes 4.Hydrothermal

1.Partial melting (solid to liquid): different minerals melt at different temperatures, changing magma composition, affecting rock formation melt 1st: minerals with low melting temp. (high silica) melt 2nd: minerals with high melting temp. (low silica) Mineral Formation: Formation From magma

2. Fractional crystallization (liquid to solid): different minerals crystallize at different temperatures, removing elements from magma, changing composition, changing rock formation Crystallize 1st: minerals with high melting point (low silica) Crystallize 2nd: minerals with low melting point (high silica) Mineral Formation: Formation From magma

What two processes cause minerals to form from magma? How do these two processes create new minerals?

High Si Low Si Higher temp Lower temp Granite formation Quartz Mica Feldspar

Geothermal gradient: As depth increases, pressure increases and melting temp increases. Why? Mineral Formation: Pressure/temp 3. Pressure and Temperature = mineral can form from changes in temp. and changes in pressure

4. Hydrothermal solutions = minerals that are formed from very HOT water. A. process involves chemical reactions within the hot water. Ex. Sulfur, bornite, chalcopyrite B. as the water cools it crystallizes. Ex. Quartz, pyrite bornite chalcopyrite Sulfur

a.Carbonates = minerals composed of carbon and oxygen normally in the form of calcite or dolomite limestone is the most common rock Calcite = Shells from organisms dissolve to help form Dolomite= magnesium chemically replaces some of the calcium Mineral formation: 2. Precipitation Precipitation = formation of minerals from water

Dolomite mountains: Italy

Mineral Formation: Precipitation Tufas = Calcium carbonate spires mono lake

Mineral Formation: Precipitation Tufa = Calcium carbonate Spheres and Barrels Pyrimid lake

2. Evaporates = minerals form when water evaporates, examples: gypsum, halite Gypsum Halite Name two locations where you know evaporates have formed. Mineral Formation: Precipitation

Salt precipitation on the great salt lake

6 mineral groups 1.Silicates 2.Carbonates 3.Oxides 4.Sulfides and sufites 5.Halides 6.Native elements

Si (silicon) + O (oxygen) Building block to silicate minerals: silicate tetrahedron (SiO 4 ) 96% of minerals in Earth’s crust, form as magma cools greater the silicon content faster it melts Lower the silicon content slower it melts 1. Silicates = minerals made of silicon and oxygen

Silicates: Quartz pure SiO 2 3-dimensional atomic structure Mica & Biotite atoms join to form sheets

2. Carbonates = minerals made up of carbon and oxygen and one other metallic element Calcite CaCO 3 Calcium Carbonate Most common Dolomite (CaMgCO 2 ) 3 ) Calcium Magnesium Carbonate

3. Oxides = contain oxygen and one or more other elements usually metals Hematite Fe 2 O 3 iron oxide Form when exposed to water

4. Sulfates & Sulfides= minerals that contain sulfur and tend to be formed by hydrothermal processes. Galena & pyrite are sulfides that from thermal or hot water solutions Gypsum is a sulfate that forms when mineral rich water evaporates

5. Halides = contain halogen ions plus one or more other elements Halite form when an Na + ion combines with an Cl - ion

6. Native elements: exist in pure form Many metals are native elements Pure C forms what native Element?

A little chemistry Minerals = compounds and elements Compound = made of several elements Element = a fundamental material consisting of one type of atom

A little chemistry What is an atom made of? An element is composed of atoms

A little chemistry An Atom is composed of: 1. Protons (+) 2. Neutrons (0) 3. Electrons (-) Atomic number = number of protons Atomic mass = average atomic weight = protons plus neutrons Isotope = same element but with a different number of neutrons How do I find the number of electrons in a atom?

Valance electrons = electrons in the outermost layer. generally, 8 is the happy number and… everything wants to be happy! What are valance electrons How many valance electrons does ___________have? If the atom has more than four valance electrons, it wants more… If the atom has less that four valance electrons, it wants to give them away Does _______ want to give away or receive electrons?

Valance electrons and Bohr models

A little more chemistry BONDING 1.Ionic bonding = electric force of attraction between a positive and a negatively charged ion. One atom gives its electrons to another, creating two charged ions. Normally occurs between two elements on opposite side of the periodic table

2. Covalent bonding = atoms are held together by their mutual attraction for shared electrons A little more chemistry BONDING Occurs most when two atoms that both want electrons come in contact with each other Molecule = atoms held together by covalent bonding

Valance electrons, bonding and Bohr models

How does bond type affect mineral properties?

Chemical and physical changes Physical properties = No change in chemical compositions Color, hardness, density, texture, phase Chemical properties = properties that relate to how substances react with one another. Involves chemical changes and chemical reactions Chemical changes = re-arrangement of the way atoms are bonded Chemical reactions = new materials are formed by a change in the way atoms are bonded

Chemical and physical changes What minerals forming processes involve chemical changes? The majority of our identification tests involve what type of properties?

What does chemistry, atoms and bonding have to do with minerals?