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Earth Science, 11e Minerals: Building Blocks of Rocks Chapter 2

Minerals are essential: They ’ re every manufactured product They ’ re essential to good health Knowledge of minerals enables us to understand earth processes

Minerals: the building blocks of rocks  Definition of a mineral: What are the 5 characteristics that make a mineral? Natural (found in nature) Have a definite chemical composition (chemical formula) Possess an orderly internal structure of atoms (A.K.A. crystal structure) Solid Inorganic (never living) Mineraloid - lacks an orderly internal structure

Composition and structure of minerals  Elements Basic building blocks of minerals Over 100 are known What is the #1 most abundant element in the Earth ’ s crust????? Atoms Smallest particles of matter Have all the characteristics of an element

Composition of continental crust Figure 2.16

Periodic table of the Elements Figure 2.4

Simplified view of the atom Figure 2.5

How atoms are constructed  __________ central part of an atom that contains ___________ positive electrical charges ___________ neutral electrical charges  Energy levels, or shells Surround nucleus Contain __________ negative electrical charges Nucleus Protons Neutrons electrons

How atoms are constructed  _______ _________ is the number of protons in an atom's nucleus  Bonding of atoms Forms a compound with two or more elements Ionic bonds and metalic bonds _______are atoms that gain or lose electrons  ___________ Have varying number of neutrons and are radioactive Atomic number Ions Isotopes

How atoms are constructed  Isotopes Have different mass numbers – the sum of the neutrons plus protons Many isotopes are radioactive and emit energy and particles

How minerals form: 1.Underground in the magma process (most minerals) 2. Re-form deep within the earth in the pressure process. 3. Near the surface in the evaporation (of water) process

How Minerals form The Magma Process: 1.Molten (liquid) rock in a magma chamber At, near or under earth ’ s surface, rises 2. The magma begins to cool and atoms, ions and molecules form various mineral compounds. 3. The molecules of the compounds mass together to form crystals.

The Pressure Process: 1. Rock is exposed to high pressures and temperatures, and the minerals begin to break down. 2. As pressure and temperature continue, the molecules RE-FORM into new minerals. 3. The minerals are elongated in shape due to the pressure.

The Evaporation Process: 1. Ions (such as salt or calcium) are dissolved in water. 2. The water evaporates, and the ions form minerals such as halite and calcite. Examples: halite (NaCl salt) » limestone (calcite)

Minerals  Physical properties of minerals Crystal form Luster Color Streak Hardness Cleavage

The mineral quartz often exhibits good crystal form

Factors that determine crystal formation: 1.Time 2.Space 3.Evaporation Rate 4.Dissolved Materials 5.Temperature 6.Pressure Largest uncut diamond found in the Letseng Mine in southern Africa. A near-flawless white gem weighing nearly 500 carats. It was discovered on Sept. 8, 2008 It weighs 478 carats, with very few inclusions and of outstanding color and clarity.

MexicoMexico's Cueva de los Cristales (Cave of Crystals) contains some of the world's largest known natural crystals—translucent beams of gypsum as long as 36 feet (11 meters). Volcanic activity that began about 26 million years ago created Naica mountain and filled it with high-temperature anhydrite gypsum. When magma underneath the mountain cooled and the temperature dropped, the anhydrite began to dissolve and for millions of years have been deposited in the caves in the form of huge selenite gypsum crystals.

1. TIME and mineral formation The RATE at which the molten magma cools determines the crystal size.

If the magma has a lot of time and it cools s-l-o-w-l-y then the crystals will…. * (example: granite) LARGE and well-formed

If the magma cools quickly, then the crystals will…. *example: obsidian has a glass-like structure Small / microscopic / not well-formed

Classzone Internet Investigation ES0506 “ How Do Crystals Grow? ” 2. Space 3. Evaporation rate 3. Amount of dissolved materials 3. Temperature 4. Pressure

Summarize in a sentence: So…. To grow the biggest, best synthetic diamond crystal, you would…. time, space, cooling rate (temperature) pressure

Pyrite (fool ’ s gold) displays metallic luster Figure 2.10

Figure 2.12 Mohs scale of hardness

Minerals  Physical properties of minerals Fracture Specific gravity Other properties Taste Smell Elasticity Malleability

Minerals  Physical properties of minerals Other properties Feel Magnetism Double Refraction Reaction to hydrochloric acid Fluorescence (UV)

Some rocks and minerals “ glow ” under UV (black) light

Minerals  A few dozen minerals are called the rock-forming minerals The eight elements that compose most rock-forming minerals are… OXYGEN (O) (46.6% by weight) SILICON (Si), (27.7% by weight) aluminum (Al), iron (Fe), calcium (Ca), sodium (Na), potassium (K), and magnesium (Mg)

Composition of continental crust Figure 2.16

?????? How can it be that… oxygen (a gas) and silicon (a metalloid) are the #1 and #2 most abundant elements in the earth ’ s crust?

Minerals  Mineral groups Most common Rock-forming mineral group is the: Silicates Contain the silicon-oxygen tetrahedron (molecule) Four oxygen atoms surrounding a much smaller silicon atom

Silicon-oxygen tetrahedron (SiO 4 ) -4 molecule Figure 2.17

Minerals  Mineral groups Rock-forming silicates Combines with other atoms to form the various silicate structures Groups based upon tetrahedral arrangement Olivine – independent tetrahedra Pyroxene group – tetrahedra are arranged in chains Amphibole group – tetrahedra are arranged in double chains

Minerals  Mineral groups Rock-forming silicates Groups based upon tetrahedral arrangement Micas – tetrahedra are arranged in sheets Two types of mica are biotite (dark) and muscovite (light) Feldspars - Three-dimensional network of tetrahedra

Hornblende – a member of the amphibole group

Minerals  Mineral groups Rock-forming silicates Groups based upon tetrahedral arrangement Feldspars Two types of feldspar are Orthoclase and Plagioclase Quartz – three-dimensional network of tetrahedra

Three examples of perfect cleavage – fluorite, halite, and calcite

Conchoidal fracture Figure 2.15

Potassium feldspar

Plagioclase feldspar

Minerals  Mineral groups Rock-forming silicates Feldspars are the most plentiful mineral group Crystallize from molten material Nonsilicate minerals Major groups Oxides Sulfides

Minerals  Mineral groups Nonsilicate minerals Major groups Sulfates Carbonates “ Native ” elements

Native Copper

Minerals  Mineral groups Nonsilicate minerals Carbonates A major rock-forming group Found in the rocks limestone and marble Halite and gypsum are found in sedimentary rocks Many have economic value

Minerals  Mineral resources Reserves are already identified deposits Ores are useful metallic minerals that can be mined at a profit Economic factors may change and influence a resource

An underground halite (salt) mine

Mineral Gemstones A gemstone is defined as… Precious? semi-precious?

Tumbled “ Gems ” Stones

Gems are valued for their reflective properties due to the way they cut (facets).

Topaz Rough – uncut – unpolished

Malachite Raw formcut and polished

Turquoise Natural turquoisejewelry

Opal Raw form

End of Chapter 2