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Minerals. What are Minerals. All the rocks and minerals in the Earth’s lithosphere are made of elements, but not all rocks are minerals . To be classified as a mineral it must be: A solid Naturally occurring Inorganic Have a crystal structure Has a definite chemical composition.
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What are Minerals All the rocks and minerals in the Earth’s lithosphere are made of elements, but not all rocks are minerals. To be classified as a mineral it must be: • A solid • Naturally occurring • Inorganic • Have a crystal structure • Has a definite chemical composition.
Minerals There about 4000 known minerals, however of all the elements in the Earth’s crust, only a mere eight make-up 98.5% of the crust total mass. Of those eight elements, more 90% of the minerals are compounds containing only two. • Oxygen – 46.6%5. Calcium – 3.6% • Silicon – 27.7%6. Sodium – 2.8% • Aluminum – 8.1% 7. Potassium – 2.6% • Iron – 5% 8. Magnesium – 2.1%
How do minerals Form? The formation of minerals is a process known as crystallization. There are three main ways minerals crystallize: • Magma Process • The Pressure Process • Crystallization from solution
Magma Process Convection currents deep in the Earth’s mantle cause magma to rise and begin to cool. As the magma cools, atoms, molecules, and ions arrange themselves into regular, repeating patterns and bond forming various crystals.
Pressure Process • Pressure chemically breaks down the rock • Heat and pressure change the rock’s properties without melting the rock • The atoms, ions, and molecules recombine to form new minerals
Crystallization From Water When water cools or evaporates, the particles of dissolved minerals come together again and crystallize.
Mineral Identification Every mineral has a unique set of physical properties that are used to identify it. These properties include: • Color • Luster • Hardness • Streak • Cleavage • Fracture • Density • Specific Gravity
Color Color is the easiest of all properties to observe however, it is the least reliable.
Luster Luster describes the way a mineral surface reflects light. Lusters include: • Metallic • Nonmetallic • Greasy • Dull • Earthy • Glassy • Pearly
Hardness Hardness is a mineral’s resistance to being scratched. Mineralogist Friedrich Mohs devised a numeric scale to determine the hardness of a mineral.
Streak The streak of a mineral is the color of its powder. Streak is obtained by rubbing the mineral on a streak plate.
Cleavage Cleavage is a mineral’s tendency to split along smooth, flat surfaces.
Fracture Fracture occurs when a mineral breaks along rough or irregular surfaces.
Conchoidal Fracture Special type of fracture that occurs in glassy type minerals.
Density Many minerals have similar densities however, very high or low densities can be used to identify certain minerals. Examples: Pumice: .64 g/cm3 Platinum: 21.5 g/cm3 Formula:
Specific Gravity A mineral’s specific gravity is the ratio of its dry mass to the mass of an equal volume of pure water. In general, the specific gravity of a mineral tells you how many times denser the mineral is than pure water. Formula: Specific Gravity = ______Dry Mass______ (Dry Mass) – (Wet Mass)
Special Mineral Properties Some minerals have unusual characteristics that can be used to identify specific minerals.
Double Refraction Double Refractionoccurs when a single light wave is split into two. Example: Iceland spar
Fluorescent When certain minerals are exposed to ultraviolet light they will glow.
Taste Minerals such as calcite and halite have a salty taste.
Magnetic Minerals such as lodestone and magnetite are naturally magnetic.
Radioactivity Some minerals such as carnotite and uraninite give off radiation that can be detected using a Geiger Counter.
Mineral Groups Minerals are classified according to similarities in composition. Minerals are classified into four main groups: • Silicates • Carbonates • Oxides • Sulfides
Silicates Silicates are any minerals that contain silicon and oxygen. The basic building block of a silicate is the silica tetrahedron.
Major Silicates cont. The feldspar family makes up approximately 60% of Earth’s crust The molecular difference between quartz and feldspar is that the silicone atom is replaced by either an aluminum, potassium, sodium, or calcium atom. Feldspar is classified into two main groups: • Orthoclase Feldspar: Potassium atom • Plagioclase Feldspar: Sodium-calcium atoms
Silicate Pyroxene Family: Ferromagnesian
Silicate Mineral in the mica family are soft silicates: Muscovite and Biotite are minerals that form flat crystals that cleave in only one direction to form thin sheets.
Carbonates A carbonate is a mineral made of negatively charged carbonate ions bonded to a positive metal ion. Each carbonate is composed of 1 carbon atom and 3 covalently bonded oxygen atoms.
Oxides and Sulfides Oxides are any mineral containing significant amounts of iron and oxygen. Sulfides are any mineral containing significant amounts of iron and sulfur. Oxides and sulfides are used in manufacturing to make steel, medicines, cosmetics, plastics, and paints. Any mineral that can be sold for a profit is known as an ore.
