Minerals

Minerals: Building blocks of rocks To be considered a mineral, a substance must: be a naturally occurring solid be formed by inorganic processes have a crystalline structure (orderly molecular arrangement) have a specific chemical composition

An element is a substance that cannot be broken down into simpler substances by chemical means Minerals are made up of one or more elements

Most abundant elements of the continental crust Common rock-forming minerals are mostly chemical compounds made up of these elements How do these elements combine to make minerals?

Atoms, molecules and ions Atoms are the smallest individual particle that retains the distinctive chemical properties of an element. Molecules are the smallest individual particle that retains the distinctive chemical properties of a chemical compound. Molecules consists of 2 or more atoms. Ions are atoms or molecules that have a net electrical charge. They attract oppositely-charged ions to form chemical compounds.

Crystalline Nature of Minerals Crystal: any substance whose atoms are arranged in a regularly repeating pattern Crystal growth is often interrupted due to: lack of space rapid cooling rate

Luster: Appearance of a mineral in reflected light Metallic (pyrite) Nonmetallic: glassy/pearly (potassium feldspar)

Luster: Appearance of a mineral in reflected light Nonmetallic- waxy (ex: chert) Nonmetallic –greasy (quartz)

Color Often highly variable for a given mineral due to slight impurities in crystal structure For example, quartz (SiO2) exhibits a variety of colors

Other Physical properties of minerals Streak Color of a mineral in its powdered form Helpful in distinguishing different forms of the same mineral Hardness Resistance of a mineral to abrasion or scratching All minerals are compared to a standard scale, the Mohs Scale of Hardness.

Streak – the color of a powdered mineral Figure 2.10

Hardness Resistance of a mineral to abrasion or scratching All minerals are compared to a standard scale called the Mohs scale of hardness

Cleavage Tendency to break along planes of weak bonding Produces flat, shiny surfaces Described by resulting geometric shapes, and Number of planes Angles between adjacent planes Cleavage is one of the physical diagnostic properties of minerals. To cleave means to break and cleavage is the tendency of a mineral to break along planes of weak chemical bonding, which we call cleavage planes.If a mineral breaks along a cleavage plane, it produces flat, shiny surfaces. If it breaks along a non-cleavage plane, the result will be jagged and irregular.

Three examples of perfect cleavage – fluorite, halite, and calcite Imagine every mineral as a 3 dimensional shape. Each plane is represented by 2 sides (top and bottom, front and back, left and right. Copyright © 2006 Pearson Prentice Hall, Inc.

Common cleavage directions Cleavage is described by the number of cleavage planes the angle between adjacent planes and the shape of the mineral if it breaks along cleavage planes

Classification of Minerals Rock-forming minerals Common minerals that make up most of the rocks of Earth’s crust Only a few dozen members Composed mainly of the 8 elements that make up over 98% of the continental crust

8 most common elements

Classification of Minerals In most cases, minerals are grouped according to the major “building block” in the chemical structure. Silicates (SiO44-) Oxides (O22-) Sulfides (S2-) Sulfates (SO42- ) Carbonates (CO32-) Halides (Cl1- , F1- Br1- ) Native Elements (single element)

Rock-forming Minerals – The Silicate Group Most common mineral group due to large amounts of silicon and oxygen in Earth’s crust Basic building block is the silicate ion: Four oxygen ions surrounding a much smaller silicon ion. Polymerization: process by which silicate ions bond to form more complex ions, such as rings, chains, sheets or 3 dimensional frameworks.

Common Silicate minerals Olivine Group http://www.youtube.com/watch?v=wFRB6T4AJbs High temperature Fe-Mg silicate Individual silicate linked together by iron and magnesium ions Forms small, rounded crystals with no cleavage

Common Silicate minerals Pyroxene Group http://www.youtube.com/watch?v=9WH_VimxA9Y Single chain structures involving iron and magnesium Two distinctive cleavages at nearly 90 degrees

Common Silicate Minerals Amphibole Group http://www.youtube.com/watch?feature=endscreen&v=fBMeVK_O3HQ&NR=1 Double chain structures involving a variety of ions linking the silicate ion Two perfect cleavages at non right angles Hornblende is the most common mineral in the amphibole group

Common Silicate Minerals Mica Group http://www.youtube.com/watch?v=EQKXqeQFyBU Sheet structures that result in one direction of perfect cleavage Biotite is the common dark colored mica.

Common Silicate Minerals Mica Group http://www.youtube.com/watch?v=_QJgwqMwXM8 Sheet structures that result in one direction of perfect cleavage Muscovite is the common light colored mica.

Classification of Minerals Common Silicate minerals Feldspar Group Most common mineral group 3-dimensional framework that exhibits two directions of cleavage at 90 degrees (potassium feldspar) (e.g. Orthoclase or Microcline) Plagioclase (sodium and calcium feldspar) are the two most common members

Feldspar Minerals http://www.youtube.com/watch?v=zGyaM29yxKI&feature=related

Potassium feldspar - Orthoclase Copyright © 2006 Pearson Prentice Hall, Inc.

Calcium-rich plagioclase feldspar http://www.youtube.com/watch?v=eWSpnr9QX74

Quartz Consists entirely of silicon and oxygen (SiO2). This is a material called silica. Strong bonds in all directions – cleavage absent. Naturally clear, but impurities cause colors. http://www.youtube.com/watch?v=kJkkmyGxcQk

Chert – Cryptocrystalline Quartz

Nonsilicate mineral groups Fluorite (left, calcium fluoride) and halite (right, sodium chloride) are members of the Halide mineral group. The minerals in this group have, as part of the chemical structure, an ion from the halogen elements: Fl1- , Cl1- , I1- , or Br1- . Gypsum (calcium sulfate) is a member of the sulfate group. The building block for minerals in this group is the sulfate ion, SO42- .

The Carbonate Group Carbonates are minerals found in exoskeletons of marine organisms. Calcite (calcium carbonate – CaCO3) is the most important carbonate mineral. It has a nearly perfect rhomboid cleavage It will dissolve if exposed to acid (as shown in the video). “Strong bones, strong teeth”

Nonsilicate Rock-forming mineral groups Sulfates – minerals containing the sulfate ion Gypsum (Calcium sulfate: CaSO4 – 2H2O. A product of rapid evaporation of ancient seas.