Minerals

Standards/Objectives  Define and describe minerals  Describe the composition and structure of minerals  Describe how minerals form  Describe the physical properties used to identify minerals

What is a Mineral?  Mineral – is a naturally occurring, inorganic solid with a definite chemical composition and crystalline structure.  There are about 3800 known minerals, ~200 are common.  They are the building blocks of rocks.

How do Minerals Form?  From the process of crystallization – the atoms of a gas or liquid come together to form a solid mineral. The atoms are arranged in an ordered three-dimensional array that is repeated in all directions. The atoms are arranged in an ordered three-dimensional array that is repeated in all directions. The crystal grows as more atoms are added onto the structure. The crystal grows as more atoms are added onto the structure.

How do Minerals Form?  Minerals can form from a magma as it begins to cool below its melting point. Ex: olivine and feldspar. Photo: Photo: directory/f/feldspar/feldspar.html

How do Minerals Form?  Minerals can form as liquids evaporate from a solution (like the crystals you made in lab). This process is called precipitation (the minerals “fall” out of the solution like rain falls out of the sky). Ex: halite forms from salt lakes

How do Minerals Form?  Minerals can also form by deposition – when a solid is formed from a gas. Ex: sulfur forms from volcanic gas Photo: imagearchive/volcanics1.htm Photo: science/photos/minerals/

Chemical Composition of Minerals  Minerals are made of elements Elements cannot be broken into simpler substances by ordinary chemical means. Elements cannot be broken into simpler substances by ordinary chemical means. There are 88 naturally occurring elements in Earth’s crust. There are 88 naturally occurring elements in Earth’s crust. There are 92 naturally occurring elements all together on Earth. There are 92 naturally occurring elements all together on Earth.

Chemical Composition of Minerals  8 elements make up 98% of the crust: Oxygen Oxygen Silicon Silicon Aluminum Aluminum Iron Iron Calcium Calcium Magnesium Magnesium Potassium Potassium Sodium Sodium

Chemical Composition of Minerals  All minerals are crystalline solids. A crystalline solid is a substance whose atoms are arranged in a regular, orderly, periodically repeated manner. A crystalline solid is a substance whose atoms are arranged in a regular, orderly, periodically repeated manner. Crystal faces (flat planes) are the external expression of the mineral’s internal atomic structure (i.e., how the atoms are arranged). Crystal faces (flat planes) are the external expression of the mineral’s internal atomic structure (i.e., how the atoms are arranged).

What makes a Mineral Unique?  There are two fundamental properties that distinguish each mineral from all others: chemical composition and crystal structure.

What makes a Mineral Unique?  A mineral’s chemical composition refers to the elements that form it.  Ex: Halite (NaCl), or table salt, is always made of a ratio of 1 sodium (Na) atom and 1 chlorine (Cl) atom.  A mineral’s crystal structure refers to the internal framework of the atoms that make up the mineral.

Crystal Forms and Systems  The general shape of a crystal (cubic, octahedral, prismatic…) is called its crystal habit If the minerals have enough space, they will form in their crystalline habit. If the minerals have enough space, they will form in their crystalline habit. Ex: quartz crystals in the shape of points. If space is limited, they will have a massive form (can’t see the crystalline habit). If space is limited, they will have a massive form (can’t see the crystalline habit). Ex: mass of quartz where can’t see individual points.

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Crystal Forms and Systems  Minerals are grouped into crystal systems based on their symmetry (i.e., the angles their faces make to one another).  There are 6 crystal systems: 1. Isometric 2. Tetragonal 3. Hexagonal 4. Orthorhombic 5. Triclinic 6. Monoclinic

Physical Properties  Are used to identify minerals.  You will be using these properties to identify minerals in the lab.

Cleavage  Cleavage – tendency of some minerals to break along a plane. There is a difference between cleavage plane (how a mineral breaks) and crystal face (how a mineral grows). There is a difference between cleavage plane (how a mineral breaks) and crystal face (how a mineral grows).

Fracture  Way in which minerals break other than cleavage (e.g., they do not break along a plane).  Types of fracture: 1. Conchoidal – smooth, curved surfaces

Fracture 2. Splintery - like ends of split wood 3. Fibrous – similar to splintery, but with a softer appearance (like worn cloth) 4. Irregular Splintery Fibrous

Hardness  Resistance of the surface of a mineral to scratching. It is controlled by the strength of the chemical bonds. It is controlled by the strength of the chemical bonds.

Hardness  Mohs hardness scale – compares the relative hardness of minerals. They are arranged in order of increasing hardness (1=soft and 10=hard).

Mohs Hardness Scale 1. Talc 2. Gypsum2 ½. Fingernail 3. Calcite3 ½. Copper penny 4. Fluorite 5. Apatite5 ½. Glass 6. Orthoclase feldspar6 ½. Steel 7. Quartz 8. Topaz 9. Corundum 10. Diamond

Specific Gravity  Weight of a substance relative to the weight of an equal volume of water. It is a measure of density (mass divided by volume or D = m/V) It is a measure of density (mass divided by volume or D = m/V) Ex: a mineral with a specific gravity of 2 weighs twice as much as the same volume of water. Ex: a mineral with a specific gravity of 2 weighs twice as much as the same volume of water.

Color  Most obvious property of minerals. Not a reliable way to identify minerals. Remember the same mineral can come in many different colors. Not a reliable way to identify minerals. Remember the same mineral can come in many different colors. The many colors of quartz

Streak  Color of the fine powder of a mineral. More reliable for identification than color. More reliable for identification than color.

Luster  How a mineral reflects light. Two main categories: Two main categories: 1. Metallic – looks like metal surface.

Luster 2. Nonmetallic – if nonmetallic, must be classified as: a. vitreous – glassy b. pearly – whitish, pearl-like iridescence c. earthy or dull

Luster d. resinous - like amber or rosin e. greasy – looks like it’s covered by a thin layer of oil (rainbow of colors)

Tenacity  Resistance of a mineral to breakage. 1. Brittle – breaks and powders easily. 2. Malleable – can be hammered into thin sheets. 3. Sectile – can be cut into thin shavings with a knife. 4. Ductile – can be drawn into a wire. 5. Flexible – bends but does not resume original shape (ex: copper). 6. Elastic – bends and regains original shape (mica).

Acid Reactivity  Effervesces (bubbles) when drop of hydrochloric acid (HCl) is placed on it.

Magnetic  Is attracted to a magnet or picks up iron filings.

Fluorescence  Emits visible light when exposed to ultraviolet (UV) radiation.

Phosphorescence  Continues to emit light after external light source is taken away.

Mineral Classifications  Silicates – minerals containing silicon (Si) and oxygen (O). Most abundant in Earth’s crust. Make up 95% of crust.  Carbonates – contain carbon (C) and oxygen (O).  Oxides – composed of oxygen and metals.  Sulfides – contain sulfur (S) and metals.  Sulfates – made up of sulfate (SO 4 - ) and metals.

Rock Forming Minerals  Silicates – are the most common minerals that make up rocks. 1. Feldspar – most abundant mineral, 50% of Earth’s crust. a. orthoclase feldspar – contains potassium (K). b. plagioclase feldspar – contains calcium (Ca) and sodium (Na). 2. Quartz – 2 nd most abundant mineral, SiO 2.

Rock Forming Minerals 3. Pyroxene – Ex: augite 4. Amphibole – Ex: hornblende 5. Mica – Ex: muscovite 6. Clay minerals – ex: kaolinite 7. Olivine