Minerals mineral = naturally occurring inorganic solid with characteristic chemical composition & crystalline

structureFive Characteristic of Minerals 1. occurs naturally 2. inorganic (not made up of living things or

remains of living things) 3. solid*4. characteristic chemical composition*5. crystalline pattern = atoms arranged in a

pattern repeated over and over* these properties are most important because they

distinguish any mineral from all others

KINDS OF MINERALS1. more than 3000 different minerals identified so far

(only 30 are common)2. rock-forming minerals = common minerals that

form the rocks of earth’s crust

3. 10 minerals make up 90% of earth’s crust: quartz, orthoclase, plagioclase, muscovite, biotite, calcite, dolomite, halite, gypsum, and ferromagnesian minerals4. classified into two main groups based on chemical composition

Minerals from magma:1. magma = molten material found beneath

Earth’s surface2. type and amount of elements in magma

determine type of minerals formed3. rate at which magma cools determines size of mineral crystals a. small crystals → cools rapidly b. large crystals → cools slowly

Mineral from solution:1. a given amount of water can only dissolve so

much of a solid2. when water becomes supersaturated (too much) with another substance, mineral crystals may

begin to precipitate out of solution3. can also be formed when water evaporates away leaving mineral behind to form crystals

halite

Mineral groups:

silicates = all minerals containing silicon and oxygen [oxygen most abundant element in crust; silicon

second most abundant]1. usually contains one or more other elements 2. most abundant - 96% of Earth’s crust 3. feldspar and quartz alone make up 50% of

earth’s crust

4. types: a. feldspars - most common 1) orthoclase = K 2) plagioclase = Na or Ca or both b. quartz = pure silicon and oxygen c. ferromagnesian minerals - rich in Fe and Mg 1) include hornblende, olivine, muscovite,

biotite

orthoclase quartzbiotite

nonsilicates = minerals that do not contain silicon1. carbonates = has carbonate groups (CO3) &

other elements

a. primary minerals found in rocks such as limestone, coquina

b. some have distinctive colorations

[azurite – blue]Ex: calcite, malachite

2. sulfates = has a sulfate group (SO4) and other elementsEx: gypsum

malachite

Gypsum crystals

3. halides = other elements with either chlorine, fluorine, iodine, and bromine

Ex: halite, fluorite4. oxides = metal element combined

with oxygenEx: hematite, magnetite

5. sulfides = metal element combined with sulfur

Ex: pyrite, chalcopyrite6. native elements = uncombined

elementsEx: copper, sulfur

copper

pyrite

fluorite

CRYSTALLINE STRUCTURE

crystal = natural solid with a definite shape1. characterized by specific geometric arrangement

of atoms2. position of atoms inside solid produce visible shape3. X-rays are used to study crystal structure

Quartz crystal

4. all silicate mineral structures have same building block a. basic unit is the silica tetrahedron

(silicon-oxygen tetrahedron) 1) silicon atom surrounded by 4 oxygen atoms 2) forms pyramid shape with silicon in middle

and oxygen at 4 corners

b. combines in different arrangements to produce different minerals

c. three types of tetrahedra arrangements 1) ionic = tetrahedrons linked only by atoms

other than Si and O 2) chains:

a) single-chain = tetrahedron bonded to two others by shared oxygen atoms

- called pyroxenes b) double-chain = 2 single chains bond to each other

- called amphiboles

3) sheets = each tetrahedron shares three oxygen atoms with other

tetrahedrad. network silicates = each tetrahedron is bonded to

four neighboring tetrahedra

mineralogy = study of minerals and their propertiesmineralogists = scientists who specializes in the

study of minerals

MINERAL IDENTIFICATIONIdentification by inspection:1. color = first and most easily observed property a. only reliable for those that are the same color b. usually isn’t enough to identify a mineral c. impurities can change mineral to various

other colors Ex: corundum = colorless

corundum + Cr = rubycorundum + Co + Ti = sapphire

d. weathered surface may hide color e. need to inspect a freshly exposed surface

2. luster = describes how light is reflected from mineral’s surface

a. metallic = reflect light like polished metalEx: pyrite, galena

b. nonmetallic = do not reflect much light 1) usually described by self explanatory

words 2) include dull (earthy), pearly, silky, brilliant,

glassy (vitreous), transparent, waxy (resinous), adamantine, greasy, and oily

3. texture = how mineral feels to the touch a. used in combination with other tests b. describe as: rough, smooth, ragged, greasy, soapy, or glassy

4. crystal habit = characteristic shape and the manner in which its crystals grow together

a. controlled by the arrangement of the atoms b. some can have more than one habit c. crystals need space to grow to develop its shape 1) when growth is obstructed the shape is

changed 2) perfectly formed crystals are rare d. crystal faces = flat surface that forms if a crystal

grows without obstruction e. six crystal systems: Table 4-1, p.78 1) defined by 3 or 4 imaginary axes

that intersect at the center of perfect crystal

2) called crystallographic axes

Identification by simple tests:1. hardness = measures how easily a mineral can

be scratched

a. controlled by strength of bonds in mineral b. measured by attempting to scratch unknown

mineral with object of known hardness 1) if object scratched unknown → unknown is

softer than object 2) if object does not scratch unknown →

mineral is harder than object

c. Moh’s Scale of Hardness = lists hardnesses of ten minerals

1) developed by Friedrich Mohs 2) softest mineral = 1, hardest = 10 3) can use these reference minerals to

determine an unknown

d. during field work use common objects to testpenny = 3.5 common nail = 4.5fingernail = 2.5 window glass = 5.5pocketknife = 5.0 steel file = 6.5

e. be sure to check for scratch since powder may rub

off from softer minerals

Mineral test kit

2. streak = color of a mineral’s powder a. obtained by rubbing mineral across piece of

unglazed white porcelain tile = streak plate b. streak will always be same color even though

color of mineral may change c. streak color can be different from color of

mineral Ex: hematite can be brown, red, or silver →

its streak is always reddish-brown

d. as a rule 1) metallic minerals generally have a dark streak 2) nonmetallic minerals will have streak that is usually colorless or very light shade of normal

colore. test works only for minerals softer than tile f. if mineral has hardness greater than 7, it will not

streak

3. way a mineral breaks a. cleavage = tendency to split easily or

to separate along flat surfacesEx: mica, fluorite

b. fracture = break with rough or jagged edges or surfaces

1) conchoidal = break into smooth, curved surfaces

Ex: quartz, obsidian 2) splintery or fibrous = leaves

a jagged surface with sharp edges

Ex: copper 3) irregular (uneven) = leaves a rough

surfaceEx: cinnabar

4. density: helps identify heavier minerals more readily than lighter ones

5. specific gravity = weight of a mineral relative to that of an equal volume of water

a. nearly all minerals are denser than water b. typical nonmetallic minerals are slightly

less than 3 c. typical metallic minerals are about 5 or greater

d. heft = determine density / specific gravity of a mineral by picking up to judge

mass 1) must practice with known minerals to develop

the feel 2) higher the specific gravity or denser minerals

will feel heavier

Formula: specific gravity = weight of sample in air

weight of equal volume of water

= weight of sample in air loss of weight in water

Example:A specimen weighs 50 newtons (N) in air and 30 N

inwater. What is the specific gravity of the

specimen?

weight in air = 50 N

weight loss = 50 N - 30 N = 20 N

sp. = 50 N = 2.5 20 N

The specimen is 2.5 times as heavy as an equal volume of water.

Unique Properties:

1. magnetism = small particles of iron - containing minerals react to magnet

Ex: magnetite - most common lodestone - acts as a magnet

2. double refraction = splits light rays into 2 parts a. one ray travels straight through and the other

ray is bent

b. causes two images to be seen when an object is viewed through transparent specimen

Ex: calcite c. refraction = bending of light rays as they pass

from one substance to another

3. acid test = specimen reacts producing bubbles

a. referred to as effervescence b. use a weak hydrochloric acid solution c. shows substance contains carbonate

Ex: calcite

4. fluorescence = ability to glow under ultraviolet light

Ex: fluorite

5. phosphorescent = continue to glow after the ultraviolet light is turned off

Ex: sphalerite

6. radioactivity = gives off radiation due to unstable nuclei decaying

a. can be detected with a Geiger counter b. pitchblende - most common mineral with

uranium c. others include carnotite, uraninite, autunite

7. taste = has a characteristic flavorEx: halite

8. smell = has a characteristic odorEx: sulfur

9. how sounds when tappedEx: jade

Mineral Uses:

ore = mineral that contains a useful substance that can be mined for a profit

Ex: hematite = iron; bauxite = aluminum

1. mines are used to remove minerals underground

2. classification of mineral as an ore can change if supply or

demand for mineral changes

bauxite

hematite

gemstones = minerals that are prized for their beauty rather than for industrial use

1. have exceptional brilliance, color, durability, and

rarity2. once cut and polished it is called a gem3. used in jewelry

4. two types: a. precious stones = rarest and most valuable

Ex: emeralds, diamonds, rubies, sapphires

b. semiprecious stones = more common, so are not as rare and valuable

Ex: amethyst, garnet, turquoise, opal

opal

5. in its natural form it may look quite different from a gem

6. different from common form of same mineral: a. elements from which it is made

Ex: manganese in quartz → purple amethyst

b. arrangement of elements → crystal structure 1) allows it to be cut and polished 2) provides information about the internal

structure7. a few gems are not minerals

Ex: pearls, amber