Download Chapter 5 Section 2 Notes

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
o weathered surfaces may hide the color of minerals
o 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
o glassy luster – appearance of glass
o waxy luster – appearance of candle wax
o pearly luster
o brilliant luster
o 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
- 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
o uneven or irregular fracture – fracture that results
in a rough surface
o splintery or fibrous fracture – fracture that results
in a surfaces that look like pieces of broken wood
o 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)
o 1 – easily scratched by a fingernail
o 2 – can be scratched by a fingernail
o 3 – barely can be scratched by a copper penny
o 4 – easily scratched with a steel file or glass
o 5 – can be scratched with a steel file or glass
o 6 - scratches glass but not steel
o 7 – easily scratches both glass and steel
o 8 – scratches quartz
o 9 – scratches topaz
o 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)
o isometric or cubic system
o tetragonal system
o monoclinic system
o orthorhombic system
o hexagonal system
o 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
o “cats-eye-effect”
o 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