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