Chapter 5 Section 1 Notes
What is a Mineral?
mineral – a natural, inorganic solid that has a characteristic chemical composition, an orderly internal structure and a characteristic set of physical properties
Characteristics of Minerals
four questions to determine a mineral
Table 1 Page 103
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Is it inorganic?
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Does it occur naturally?
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Is it a crystalline solid?
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Does it have a consistent chemical composition?
answers must be “Yes” to all to be considered a mineral
Kinds of Minerals
over 3000 minerals
fewer than 20 are common
rock forming minerals – common minerals that form the rocks that make up Earth’s crust
10 are so common, they make up 90% of Earth’s crust
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quartz, orthoclase, plagioclase, muscovite, biotite, calcite, dolomite, halite, gypsum, and ferromagnesian minerals (contains iron and/or
magnesium)
Silicate Minerals
silicate mineral – a mineral that contains a combination of silicon and oxygen and they may also contain one or more metals
quartz has only silicon and oxygen
feldspars are the most common
make up 96% of Earth’s crust
Nonsilicate Minerals
nonsilicate minerals – a mineral that does not contain compounds of silicon and oxygen
make up 4% of Earth’s crust
six major groups
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carbonates, halides, native elements, oxides, sulfates and sulfides
Crystalline Structure
all minerals have a crystalline structure
crystal – a solid whose atoms, ion or molecules are arranged in a regular, repeating pattern
scientists use X-rays to study the structure of crystals
Crystalline Structure of Silicate Minerals
each building block has four oxygen atoms arranged ina pyramid with one silicon atom in the center
silicon-oxygen tetrahedron – the basic unit of the structure of silicate minerals; a silicon ion chemically bonded to and surrounded by four oxygen ions
six kinds of silicate-mineral arrangements (Fig 3 pg 107)
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isolated tetrahedra – individual tetrahedra do not link with other silicon or oxygen atoms
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ring silicates – tetrahedra form a ring by sharing oxygen atoms
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single-chain silicates – tetrahedra form a chainby sharing oxygen atoms
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double-chain silicates – form when two sing chains of tetrahedra bond to each other
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sheet silicates – form when each tetrahedron shares three of its oxygen atoms with other tetrahedra
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framework silicates – form when each tetrahedra is bonded to four other tetrahedra
The Crystalline Structure of Nonsilicate Minerals
display a vast variety of crystalline structures
forms cubes, hexagonal prisms and irregular masses
structure of the crystal determines characteristics
native elements have very high densities
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occurs because of closest packing
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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 will allow
Chapter 5 Section 2 Notes
Identifying Minerals
mineralogist – a person who examines, analyzes and classifies minerals
mineralogists will study properties of minerals to identify them
Physical Properties of Minerals
each mineral has specific properties
properties are a result of chemical composition and crystalline structure
Color
some minerals have a distinct color
not a reliable clue for identifying a mineral
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weathered surfaces may hide the color of minerals
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inspect only the mineral’s freshly exposed surface
Streak
streak – the color of a mineral in powdered form
rub the mineral across an unglazed ceramic tile
streak color may differ from the solid form color
minerals harder than the ceramic tile will leave no streak
Luster
luster – the way in which a mineral reflects light
metallic luster – a mineral that reflects light as polished metal
nonmetallic luster – does not reflect light as polished metal
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glassy luster – appearance of glass
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waxy luster – appearance of candle wax
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pearly luster
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brilliant luster
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dull or earthy luster – lack of any luster
Cleavage and Fracture
cleavage – the tendency of a mineral to split along specific planes of weakness to form smooth, flat surfaces
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breaks along flat surfaces that generally run parallel to planes of weakness
fracture – the manner in which a mineral breaks along either curved or irregular surface
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uneven or irregular fracture – fracture that results in a rough surface
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splintery or fibrous fracture – fracture that results in a surfaces that look like pieces of broken wood
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conchoidal fracture – fractures that result in curved surfaces
Hardness
hardness – the ability of a mineral to resist scratching
does not mean “resistance to cleavage or fracture”
Mohs hardness scale – the standard scale against which the hardness of a mineral is rated (Table 1 page 111)
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1 – easily scratched by a fingernail
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2 – can be scratched by a fingernail
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3 – barely can be scratched by a copper penny
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4 – easily scratched with a steel file or glass
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5 – can be scratched with a steel file or glass
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6 - scratches glass but not steel
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7 – easily scratches both glass and steel
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8 – scratches quartz
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9 – scratches topaz
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10 – scratches everything
strength of the bonds between atoms determines hardness
Crystal Shape
certain minerals always have same general shape because they always combine in the same general pattern
six basic shapes (Table 2 page 112)
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isometric or cubic system
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tetragonal system
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monoclinic system
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orthorhombic system
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hexagonal system
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triclinic system
Density
ratio of the mass of a substance to the volume of the substance (g/m3)
depends on atom type and closeness of the bonded atoms
density helps identify heavier minerals more readily
Special Properties of Minerals
Fluorescence and Phosphorescence
fluorescence – ability of a mineral to glow under ultraviolet light
phosphorescence – ability of a mineral to continue to glow after ultraviolet light has been removed
Chatoyancy and Asterism
chatoyancy – minerals that display a silky appearance in reflected light
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“cats-eye-effect”
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a result of closely packed parallel fibers
asterism – a six sided star shape appears when a mineral reflects light
Double Refraction
refraction – the bending of light rays as they pass from one medium to another (air, light)
double refraction – production of a double image of an object when viewed through a transparent mineral
Magnetism
occurs in minerals containing iron
some minerals will produce north and south poles
Radioactivity
results as unstable nuclei decay and form stable nuclei
Geiger counter – a device used to detect radioactivity