The Building Blocks of Rocks
Jan 15, 2016
The Building Blocks of Rocks
MineralsAll minerals are made up of single elements or
compoundsElement: an element is made up of atoms, and
cannot be broken down into a simpler substance
Compound: a compound contains 2 or more kinds of atoms that are bonded (chemically joined) together
Atom: an atom is the smallest part of an element – it has all of the properties of the element, but cannot be seen – even with tools!
Definition of a Mineral – must exhibit ALL of these traits!Naturally occurring – synthetic substances are NOT
mineralsInorganic – cannot form as a result of plant/animal
activities (pearls and coal are NOT minerals)SolidDefinite chemical composition (they are composed
of distinct elements or combinations of elements)(Take a look at the last page of your ESRT!)Internal arrangement of atoms gives it a crystalline
structureDefinite set of physical properties
Quartz and the Silicon Oxygen tetrahedron
MINERAL FAMILIES Minerals can be classified according to their chemical compositions – page
16 of ESRT
OXIDES – composed of oxygen and 1 other element (not Si) – example is Hematite
SULFIDES – composed of sulfur and 1 other element – example is Galena
CHLORIDES (Halides) – composed of chlorine and 1 other element – example is Halite
CARBONATES – composed of 1 or more metals + CO3 (carbonate) – example is Calcite
SULFATES – 1 or more metals + SO4 (sulfate) – example is Selenite gypsum
SILICATES – 1 or more metals + Silicon and Oxygen – example is Quartz
Properties of Minerals for ID! These are used to identify minerals in labs or in the field!
ColorLusterStreakHardnessBreakage Pattern (Cleavage or Fracture)Density/Specific GravityCrystal ShapeSpecial properties such as odor, acid reaction,
magnetism, taste (salty), double refraction, striationsENR: Diaphaneity, Tenacity
ColorColor is a useful property only for some
mineralsFor most minerals, however, color is NOT a
useful ID tool – why?1) many minerals come in different colors2) one color, such as white, can be seen in
many different mineralsBut, color can be used to ID certain minerals
that usually exhibit only 1 color (such as sulphur, which is yellow)
So, is color useful?No!!Well, sometimes…..But it sure makes looking at minerals a LOT
more interesting, yo!
LusterThe way light shines or glares off the surface
of mineralsThis is better than color in mineral IDThis is a fairly subjective propertyYou need to become familiar with some
terms…
Luster – main propertiesMetallic: looks like metal in the way it
reflects light – examples are galena or pyrite (like polished metal) – Bling
Sub-metallic – (like unpolished metal) - BlungNon-metallic: does not look like polished
metal, so other terms are needed!
ENR- Types of Non-Metallic LusterVitreous – glassy looking, like quartzSilky – um…like silkWaxy/Resinous – dull shine like candle wax or
resin – like sulphurAdamantine – gives off a glare at a certain
angle, like a diamondDull/Earthy – no shine at all, like bauxitePearly - looks like a pearl when light reflected
off it, like garnet or opalGreasy – like soap (talc)
StreakThe color of the mineral in powder form
when it’s rubbed against a porcelain plate (called a streak plate)
Most minerals display only one streak color:Hematite always has a reddish brown streakSulphur has a yellow streakSphalerite has a yellow streakMagnetite has a black streak
HardnessThe mineral’s resistance to being scratchedWe use Moh’s Hardness Scale to determine a
mineral’s hardnessThis scale uses 10 index minerals with
hardness ranging from 1 (least hard) to 10 (hardest)
Breakage Pattern:Cleavage: the tendency of a mineral to break
along planes of weaknessFracture: no definite planes of weakness, just
breaks irregularly
Crystal ShapeCrystal shape can vary, and can be difficult to
recognize
CleavageTendency to split along flat surfaces (planes)
where the chemical bonds are weakCan be spotted when light reflects off an
entire surface simultaneouslyCan be in several directions at varying angles
Cleavage directions/angles
FractureTendency to break WITHOUT cleavage,
randomlyCan still exist in minerals that show cleavage
in other directions thoughENR:Types:Conchoidal – fracture pattern resembles a
conch shellFibrous – looks like fibersUneven – looks uneven
Fracture
Density/Specific GravityEvery mineral has a certain density, but only
sometimes is it useful for ID!A great example is the hefty mineral Galena
Acid ReactionMinerals in the carbonate family (CO3) will
react to HCl and will release CO2 bubbles (called effervescence)
ENR - TenacityResistance to crushing, bending, etc. See lab packet for types
ENR - DiaphaneityHow light is transmitted through a mineral
(or not)Transparent – full transmission of imageTranslucent – hazy light but no imageOpaque – zero, zilch, nada transmission
Special propertiesMagnetism – mineral is magnetic, like MagnetiteTaste (salty) – mineral tastes like salt, because
that’s what it is – HaliteDouble refraction – mineral will transmit an
image and will double it! Iceland Spar (a type of calcite) will do this.
Striations – tiny grooves on a cleavage plane (Plagioclase Feldspar)
SEE page 16 of the ESRT, and look in the DISTINGUISHING CHARACTERISTICS column