WHAT IS A MINERAL?Earth ScienceChapter 4Section 1
Mineral Characteristics Mineral Naturally occurring
Inorganic Solid Specific chemical
composition Definite crystalline
structure
Rock Forming Minerals 3000 minerals occur in Earth’s crust 8-10 refered to rock forming minerals
Make up most of the rocks
Minerals from Magma Magma less dense than
surrounding rocks Rises
As cools, crystals form Elements in magma determine
the mineral formed Large crystals
Cool slowly, atoms have time to arrange in large crystals
Small crystals Rapidly cooling magma
Minerals from Solution Minerals dissolved in water
Salts Saturated
Water can’t hold any more of the substance Supersaturated - Precipitates
Solution becomes overfilled Conditions right for minerals to form Individual atoms bond together and mineral
crystals form into solids from the solution
Minerals form Solutions Evaporates
Minerals crystallize when the solution evaporates
Crystal Form Distinct crystal shape
Easily recognizable Halite- cubes Quartz - double pointed ends
Perfect crystals are not the norm Crystallization should not be used as only
form of identification
Luster
Metallic luster Shiny surfaces
that reflect a lot of light
Nonmetallic luster Do not shine
Dull, pearly, waxy, silky or earthy
Metallic Luster Non Metallic Luster
Hardness Hardness is the
measure of how easily a mineral can be scratched.
Most useful and reliable of all tests
Mohs Hardness Scale used to compare minerals
Cleavage and Fracture
A mineral that splits easily alone one or more flat planes
Minerals that bread with rough jagged edges
Cleavage Fracture
Conchoidal fracture
Streak The powder left
on a ceramic plate when a mineral is scratched along it.
Does not always match the color of the mineral.
Color Most noticeable
characteristic Least reliable Sometimes
caused by trace elements or compounds within the mineral
Special Properties Magnetism Striations Double refraction
Light is split into two rays Effervescence
Does if fizz? Fluorescence
Shine in ultraviolet light
Texture How the mineral feels to the touch Subjective Used with a combination of tests
Specific Gravity Ratio of the weight of the mineral with
the weight of an equal volume of water. Specific gravity of minerals can be
roughly relatively tested using heft.
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