Minerals

http://www.mii.org/

Why are minerals important to me?

• Minerals are also the building blocks of rocks

• Three types of rocks– Igneous– Sedimentary– Metamorphic

The Rock Cycle

The Importance of Rocks and Minerals

Name Type of

Rock Use

Basalt Igneous Used in road building

materials

Calcite Mineral Used in cements and mortars and the production of

lime

Granite Igneous Used for buildings, monuments, and tombstones

Marble Metamorphic Used in building, floors, tile in bathrooms

Obsidian Igneous Used in making arrowheads and knives

Pumice Igneous Used in scouring, scrubbing, and polishing materials

Quartz Mineral Used in making glass, electrical components, and

optical lenses

Sandstone Sedimentary Used in the building industry for houses

Slate Metamorphic Used for roofs, chalkboards, and patio walks

Minerals are found in the lithosphere of the Earth.

• The crust of the lithosphere is specifically where these minerals are found. Eight elements comprise these minerals:

• Oxygen (46.6%) • Silicon (27.72%) • Aluminum (8.13%) • Iron (5.00%) • Calcium (3.63%) • Sodium (2.83%) • Potassium (2.70%) • Magnesium (2.09%).

• The oceanic crust has more Silicon, Oxygen, and Magnesium. The continental crust has more Silicon and

Aluminum.

(picture from Glencoe text, Earth Science)

Minerals: Defined

• The word “mineral” means something very specific to earth scientists. By definition, a mineral: – Is naturally formed– Is solid– Is formed by inorganic processes– Has a specific chemical composition – Has a characteristic crystal structure

Naturally formed

• Minerals form through natural processes within the earth, including volcanic eruptions, precipitation of a solid out of a liquid, and weathering of pre-existing minerals

Solid

• Liquids and gases are not considered minerals, in large part because their structure is constantly changing, which means they do not have a characteristic crystal structure.

Formed by inorganic processes

• Any material produced through organic activity – such as leaves, bones, peat, shell or soft animal tissue – is not considered a mineral

• Fossils, although they were once living, have generally had their living tissues completely replaced by inorganic processes after burial; thus, they are considered to be composed of minerals as well.

Identification of Minerals

Minerals can be identified by specific chemical and physical properties.

Specific Chemical Composition

• Most minerals exist in the earth as chemical compounds whose compositions can be expressed using a chemical formula.

NaCl or Sodium chloride = salt

Crystal Structure

• The chemical composition of a mineral is reflected internally in a regular, repeating arrangement of atoms, called the crystal structure of the mineral.

Crystal Structure

• A crystal is the solid form of a substance in which the atoms or molecules are arranged in a definite, repeating pattern.

Crystal Structure

• The formation results in one of three ways: dissolved matter may precipitate out of a solution such as molten magma or sea water; gases may condense into a solid form, and two or more solid crystals under high temperature and pressure may recombine into a new mineral.

Crystal Structure

Large crystals can form from slow cooling of magma (intrusive igneous rock).

Small crystals can form from rapid cooling of magma (extrusive igneous rock).

Andesite Obsidian

The external shape of the crystal -- smooth, symmetrically arranged, flat surfaces -- reflects its atomic structure.

Crystaline structure of salt

Crystal Formation

• Minerals grow in specific shapes, and usually crystallize into one of six crystal systems. The axes of the crystal, the angles at which the axes intersect, and the degree of symmetry define each system.

Types of Crystals

• Isometric (AKA cubic crystal system) Crystals are usually shaped like blocks, with similar and symmetrical faces. The crystal has three axes of symmetry, all at right angles to each other, and all of the same length.Example: pyrite.

• Tetragonal -- Typically, the crystals are shaped like four-sided prisms and pyramids. Each crystal has three axes, all perpendicular to one another. Two axes are the same length and lie on a horizontal plane. The third axis is not the same length and is at a right angle to the other two.Example: zircon.

Types of Crystals

• Hexagonal -- These crystals are usually shaped like six-sided prisms or pyramids. Each crystal has four axes of symmetry. Three lie in the same plane, are the same length, and intersect at 120° angles. The fourth axis is not the same length, and is perpendicular to other three.Example: beryl.

• Orthorhombic -- These crystals are short and stubby. Each crystal has three unequal axes, all at right angles to one another.Example: topaz

Types of Crystals

• Monoclinic -- Crystals are short and stubby with tilted faces at each end. Each crystal has three unequal axes. Two axes lie in the same plane at right angles to each other. The third axis is inclined.Example: gypsum.

• Triclinic -- Crystals are usually flat with sharp edges, but exhibit no right angles. Each crystal has three unequal axes. None are perpendicular to one another. Example: feldspar.

Other Chemical Properties

• Fusibility- ease with which a mineral melts– Stibnite (antimony trisulfide):will melt in a

match flame

• Flame coloration - color a mineral will give off when placed in a flame– Depends on elements in mineral

Diagnostic Characteristics of Minerals

Properties of Minerals

• Color• Streak• Luster• Hardness• External crystalline form• Cleavage• Fracture• Specific Gravity

Color

• Color can be true or caused by an impurity in the mineral.– Examples:

Graphite- black

Pyrite - brassy yellow

Malachite- green

Streak

• The color of a mineral in fine powder form.

– Requires a streak plate.

Luster

• Luster is the way the surface of a mineral reflects light.

• Luster should be observed on a cut or freshly broken, untarnished surface.

• There are two general types of luster -- metallic and non-metallic.

Luster

• The terms used to describe luster are:– Metallic -- example: gold – Vitreous (glassy) -- example: quartz, tourmaline – Adamantine (brilliant) -- example: diamond – Resinous (like resin or sap from a tree) -- example:

sphalerite – Greasy or waxy -- example: turquoise – Pearly -- example: talc – Silky -- example: asbestos – Dull or earthy -- example: bauxite

Luster

Examples of only a few of the different lusters that can be seen in minerals. Galena (on the left) has a metallic luster, amber (in the middle) is resinous, and quartz (on the right) is glassy.

Hardness

• The hardness scale was established by the German mineralogist, Friedrich Mohs.

• The Mohs’ hardness scale places ten common or well-known minerals on a scale from one to ten.

http://www.sodablastingservices.com/images/mohsscale.jpg

http://www.allaboutgemstones.com/mohs_hardness_scale.html

Quick and Easy Moh’s

A more limited but practical scale can be easily and cheaply obtained by observing that

....your fingernail has a hardness of 2.5, ....a penny has a hardness of about 3.5,

....glass and a steel nail have nearly equal hardnesses of 5.5 and ....a streak plate has a hardness of 6.5.

Hardness

• Some minerals' hardness may vary from sample to sample depending on that mineral's exact chemical composition

• Testing the hardness of rocks is less effective than testing the hardness of minerals. – A rock is basically a mixture of various

minerals, although it can contain non-mineral materials such as natural glass and fossils.

Hardness

• The hardness or rocks and minerals is also dependent on the degree of weathering.

Hardness- caution

• Hardness depends on the strength of the bonds holding the mineral together.

• The bond strength can be significantly different in different directions in the mineral, giving the different hardness.

• In most minerals this difference with direction is minor and doesn't affect the test.

Cleavage

• Some minerals have weak bonds along certain planes. They break when hit with a hammer into shiny, flat, surfaces.

• It is sometimes important to also take note of the angle between the cleavage directions.

Cleavage Crystal form

• When a mineral exhibits cleavage, it will break into pieces that have the same geometry as each other.– Example is quartz crystals- they form pieces

that are not identical when broken

Cleavage types

• Perfect- only a light tap of hammer is needed

• Distinct - requires a heavier hammer tap

• Conchoidal fracture - surfaces are not flat but rounded, like a clam shell

Specific gravity/Density

• “How much heavier is the mineral than water?”

Specfic gravity/Density activity SPECIFIC MINERAL

GRAVITY NAME

3.3 -4.3 GOETHITE

3.9 - 4.1 SPHALERITE

2.8 - 3.2 BIOTITE

7.4 - 7.6 GALENA

2.23 GRAPHITE

5.02 PYRITE

5.56 HEMATITE

5.18 MAGNETITE

4.58 - 4.65 PYRRHOTITE

4.1 - 4.3 CHALCOPYRITE

5.0 -5.1 BORNITE

Tenacity Descriptions

• Brittle

• Malleable

• Ductile

• Sectile

• Flexible

• ElasticMica is very elastic.

Magnetism

• For some minerals, the powdered form is magnetic, but not larger pieces.

Mineral Groups

http://www.minsocam.org/MSA/K12/groups/images/group.gif

Silicates

• Silicates all contain the silicon and oxygen in some proportion.

http://www.indiana.edu/~geol116/week2/mineral.htm

Silicates

• Silicates are by far the most common minerals in the earth’s crust and mantle comprising 95% of the crust and 97% of the mantle, by most estimates.

• Silicates also have a wide variety of physical properties, despite the fact that they often have very similar chemical formulas.

Beryl- Berylium Aluminum Silicate

Silicates

• Despite the fact that there are many hundreds of silicate minerals, only about 25 are truly common. Therefore, by understanding how these silica tetrahedra form minerals, you will be able to name and identify 95% of the rocks you encounter on the surface of the earth.

Silicate Structure

Silicates

Three ways of drawing the silica tetrahedron: a) At left, a ball & stick model, showing the silicon cation in orange surrounded by 4 oxygen anions in blue; b) At center, a space filling model; c) At right, a geometric shorthand.

Silicates

• Isolated tetrahedra: Olivine

Silicates

• Chains of tetrahedra: Pyroxenes and amphiboles – forming long chain structures

Silicates

• Double chains form when every other tetrahedron in a single chain shares a third oxygen ion with an adjoining chain

Hornblende

Silicates

• Sheets: Micas and clays – When every tetrahedron shares three of its

oxygen ions with neighboring tetrahedra, sheets are formed

Biotite is the mineral on the left, muscovite is on the right; both are micas, which are one kind of sheet silicate.

Silicates

• Framework: Quartz and feldspar – When each tetrahedron shares all of its

oxygen atoms with adjacent tetrahedra, a very strong 3-dimensional framework of Si-O bonds is formed

The white, blocky minerals in the rock on the left are plagioclase feldspar; the pink minerals in the rock on the right (granite) are K-feldspar.

Common Silicates

Common Silicates

Non silicates

Most common:

• Oxides

• Sulfides

• Carbonates

Oxides

• One or more metallic elements combined with oxygen, water, or hydroxyl group (OH)

Corundum (Al2O3)- ruby Corundum- sapphire

Oxides

• Many oxides (hematite and magnetite) and hydroxides (limonite and goerthite) of iron are important minor constituents in rocks.

• The aluminum oxide bauxite can also occur as a rock-forming mineral.

• Oxide minerals are exploited as economic sources of many elements including aluminum, antimony, iron, manganese, tin, and uranium

Sulfides

• Sulfur ions (S2- ) bind with a number of positive ions to form the sulfide minerals.

• Common examples are:– Pyrite– Galena– Sphalerite

Galena

Pyrite

Sulfides

• Economically important class of minerals.

• The mineral pyrite is the only sulfide that occurs commonly in rocks.

• Sulfides are most important as economic minerals providing the main sources of elements such as arsenic, copper, lead, nickel, mercury, molybdenum, sliver and zinc

Halides

• The halides are a group of minerals whose principle anions are halogens. Halogens are a special group of elements that usually have a charge of negative one when chemically combined.

• The halogens that are found commonly in nature include Fluorine, Chlorine, Iodine and Bromine.

• Halides tend to have rather simply ordered structures and therefore a high degree of symmetry.

Halides

Typical properties:– Soft– Transparent– Not very dense– Good cleavage– Often bright colors

Fluorite- Calcium fluoride

Halite- Sodium chloride

Halide minerals

• Halite- NaCl

• Sylvite - KCl

• Fluorite- CaF2

• Cryolite- Na3AlF6

Sulfates

• Typical properties– SO4

-2 anion

– Soft– Light in color– Low densities– Some are fluorescent

Gypsum- hydrated calcium sulfate

Sulfate minerals

• Gypsum

• Celestine

• Anhydrite

• Barite

• EpsomiteAnhydrite - Calcium sulfate

Carbonates

• Typical properties– Carbonate ion (CO3 -2) gives these minerals

their properties– Form well developed rhombohedral crystals– Dissolve easily in HCl– Colorless or vividly colored

Calcite

Carbonate minerals

• Calcite

• Dolomite

• Malachite

• Azurite

Dolomite

Malachite

Native elements

• Carbon– Diamond– Graphite

• Sulfur

• Copper

• Silver

• Gold

• Platinum

Gold

Carbon- graphite