The universe (nature, cosmos) consists only of matter and energy.

Matter has four significant properties:

1. Matter has substance, the measure of which is termed mass.

2. Matter occupies space, the mesure of which is termed volume.

3. Matter attracts other matter by a force called gravity; the force is directly proportional to the product of two masses and inversely proportional to the square of the distance between two masses.

4. Matter can be converted into energy.

Matter is found in each of three states: solid, liquid, and gas.

Matter and energy are composed of tiny particles. The most important such particles are called atoms. Atoms are the smallest units of matter that retain the characteristics of elements. Elements are the chemical building blocks of matter; each element has its own peculiar type of atom. Atoms themselves are made of even tinier particles called subatomic particles, the most important of which are protons, neutrons, and electrons. There are dozens of other subatomic particles which we will not study.

A proton has an electric charge of +1 and a rest mass of 1.67 x 10-24 gm. A neutron has a charge of 0 and a rest mass of 1.67 x 10-24 gm. (about the same as a proton). An electron has a charge of -1 and a rest mass of 9.11 x 10-28 gm. (much, much less than a proton). The important point here is that the electron mass is negligible relative to protons and neutrons.

The heavy particles (protons and neutrons) are bound into the nucleus, whereas the electrons form complex orbitals about the nucleus.

The chemical properties of an element depend on the number of protons (i.e. the net electric charge) of the nucleus. The number of protons in the nucleus is known as the atomic number of the element. Atomic numbers for natural element range from 1 (hydrogen) to 92 for uranium.

The number of protons plus neutrons in the nucleus is known as the mass number of the atom. Atoms of a given element (atomic number) may have differing numbers of neutrons. Atoms of the same element with different mass numbers are known as isotopes. The mass numbers or isotopes of an element are denoted as preceding superscripts. For example the stable isotopes of the element oxygen are denoted 18O, 17O and 16O. Oxygen has an atomic number of 8 (eight protons). The nucleus of 16O thus contains eight protons and eight neutrons. How many neutrons are in the nucleus of 18O? (ans.: 10). Because elements may have several stable isotopes, the average mass number of an element is the atomic weight and is commonly not an integer.

Atoms may not change their atomic numbers or mass numbers except by very energetic nuclear reactions. However atoms may gain or lose electrons in ordinary chemical reactions. If an atom has the same number of electrons as protons, it is a neutral atom. If it has a net charge, (more or less electrons than protons) it is an ion. If it has more electrons than protons it has a net negative charge and is known as an anion. If it has fewer electrons than protons it has a net positive charge and is known as a cation. The ionic state may be denoted as a following superscript (e.g. O2-, Fe2+). The common ionic states of a atom are known as its valences.

Because electrons arrange themselves in discreet orbitals about the nucleus and the orbitals repeat in shells, the chemical properties of the elements tend to repeat as the atomic number increases. This periodicity of properties gives rise to the periodic table of the elements.

The elements H, He, and minor amounts of Li were formed in the original Big Bang. All heavier elements were formed form the primordial H and He by nuclear fusion reactions in stars. The fusion reaction proceeds in steps in stars massive enough to undergo the full sequence. (Our sun is not massive enough to form elements more massive than He by direct fusion and will die when all the H is consumed.) First H is consumed to form He. When the H is consumed, the star collapses until He is "ignited" to form Be and C. There are many free neutrons in these reactors and nuclei will capture enough neutrons to stabilize themselves. Most of the heavy elements are formed by neutron capture rather than by direct fusion. In the last stage Fe is formed by direct fusion of Si and other light elements. This reactions is rapid and results in an explosion. Our solar system condensed from the remnants of one of these supernova explosions.

Chemical bonds may be either ionic, metallic, covalent or vander Waals (mirror charge), and the bond type preferred by the various elements will determine their geochemical affinity. Ionically bonded elements are termed lithophile and combine with the most abundant element, O, and are enriched in the silicate and oxide minerals (rocks). Metallically bonded elements are termed siderophile and combine with native iron and are enriched in the core. Covalently bonded elements are termed chalcophile and combine with sulfur and are enriched in ore minerals. The atmophile elements form only very weak vander Waals bonds and did not condense in the inner solar system. They are depleted in Earth and enriched in the outer planets.

A mineral is a naturally occurring homogeneous solid of definite chemical composition and ordered atomic arrangement. It is usually formed by inorganic processes.

More than 5000 mineral species have been described and more than 100 new minerals are described every year. To describe a new mineral, the structure and composition must be described.

Most of these 5000 minerals are rare, so that only about 200 are common enough to make up macroscopic rocks. Of these, the most abundant 50 make up 99.9% of the Earth's crust.

Some examples of minerals that are familiar to you are quartz (SiO2, silicon dioxide), calcite (CaCO3 calcium carbonate), pyrite (FeS2, iron sulfide), gypsum (CaSO4 . 2 H2O), gold (Au), silver (Ag), copper (Cu), diamond (C), graphite (C), garnet (Mg3Al2Si3O12), ice (H2O). Less familiar, perhaps, are apatite (Ca5 (PO4)3OH) (teeth and bone), olivine (Mg2SiO4) (the green mineral that makes up much of the upper mantle, gem variety: peridot), pyroxene (MgSiO3) (the other mineral in the upper mantle), muscovite (white) mica (KAl2(AlSi3)O10(OH)2), and feldspar (Na,K)AlSi3O8 or CaAl2Si3O8.

A crystal is a three-dimensional periodic array of atoms. Most solids are crystalline, but some, like glass, opal, amber, wood, and coal, are not and are said to be amorphous.

The basic repeat unit of a crystal or mineral is the unit cell.

Crystals have complex symmetries. Ice, apatite, and graphite are hexagonal (six-fold symmetry); quartz and calcite are trigonal (three-fold symmetry); diamond, garnet, gold, pyrite are cubic (three four-fold axes), olivine is orthorhombic; micas are monoclinic; and feldspars are triclinic.

A given compound like SiO2 may occur as different crystalline forms. If the crystalline structures of the two forms are different, they are said to be polymorphs.

SiO2 may occur as the mineral quartz, or, at high temperatures quartz transforms to tridymite, and then to cristobalite. If a rock containing quartz is subducted into the mantle, the quartz transforms first to coesite at a depth of about 100km, then to stishovite at a depth of about 250km. These minerals are said to be polymorphs of quartz. Graphite and diamond are polymorphs of carbon. Pyrite and marcasite are polymorphs of FeS2.

Conversely, chemical elements that have similar chemical properties may substitute for one another in a given crystal structure so that the same structure may occur with different compositions. This is called isomorphism. An example is albite (NaAlSi3O8) and orthoclase (KAlSi3O8) feldspars. In the feldspar crystal structure, Na (sodium) and K (potassium) are alkalis and can substitute freely for one another, so that all compositions between albite and orthoclase may exist.

We can use some simple observations of physical properties of minerals to distinguish or identify the most common minerals.

Hardness is the ability of a mineral to resist scratching. We use the Mohs' hardness scale for field testing: 

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1. Talc                 4. Fluorite             7. Quartz

2. Gypsum               5. Apatite              8. Topaz

3. Calcite              6. Orthoclase           9. Corundum

                                                10. Diamond

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Luster is the reflectivity of a mineral: metallic or non-metallic. Of the non-metallic minerals some may be glassy (vitreous), dull (earthy), or adamantine (bright with many internal reflections) as in diamond.

Color is simply the color of a mineral in hand specimen, but tiny amounts of certain elements like iron can strongly color a hand specimen. So the color of a powdered mineral is considered much more diagnostic. An easy way to do this test is to examine the color of the mineral's streak when scratched on a porcelain plate.

The external form or shape of crystals may be the result of fracture or of growth. When a crystal grows in a liquid (magma or aqueous fluid), its rapid growth directions become points and its slow growing directions become faces.

If a crystal has a plane of weak chemical bonds it can break along perfect planes. This is called cleavage. Mica has a single perfect cleavage whereas calcite has three. Quartz has no cleavage and breaks like glass (conchoidal fracture).

Minerals are natural molecules that make up geological materials, such as rocks. All minerals are molecules, and most are compounds. A few minerals, called native elements, are molecules of only one element. These include gold Au, silver Ag, platinum Pt, graphite C, diamond C, sulfur S, and copper Cu.

Minerals have a six-part definition:

1. Naturally-occurring

2. Inorganic

3. Solid

4. Have an ordered, internal atomic geometry in which the atoms are arranged in a regular, 3-dimensional framework; this ordered internal atomic structure makes minerals crystalline, the physical manifestation of which is called a crystal.

5. Have a specific chemical composition that varies only within narrow limits and can be expressed by a chemical formula.

6. Possess characteristic physical properties that allow the mineral to be identified.

A rock is an aggregate of minerals. Rocks can be formed by many different processes. Some are formed from melts (igneous). Some are formed by solidifying sediments like sand or clay (sedimentary). Some are formed by re-crystallizing previously formed rocks in the solid state (metamorphic). And some are formed by crystallization from hot aqueous fluids (hydrothermal).

Rocks that are formed by crystallization of a melt are igneous. These may be formed at depth (intrusive or plutonic), or they may form on the surface (extrusive or volcanic). In general, igneous rocks that cool rapidly (i.e volcanic rocks) are very fine-grained; whereas rocks that cool slowly (i.e. plutonic rocks) are coarse-grained.

Rocks that are formed on the surface of the Earth by solidfication (lithification) of weathered or dissolved material are sedimentary.   These are generally classified by the size of the particles, although the compositions change systematically with particle size.

Rocks that form by recrystallization in the solid state are metamorphic. They may be metamorphosed from sedimentary, igneous,  metamophic, or hydrothermal rocks.

Rocks that form by crystallization from hot aqueous fluids are hydrothermal. These are commonly formed near intrusive igneous bodies. This is a very efficient way to concentrate the elements of low natural abundance, so many of the economically important ore minerals are formed this way.

Magma is the term for any molten silicate material, whether below the surface or on top.

Magma that is injected and crystallized below the surface forms intrusive igneous rocks. Because they cool more slowly than extrusive rocks, intrusive igneous rocks are generally coarse-grained (>1mm). A very coarse-grained igneous rock (>2cm) is called a pegmatite.

The same compositional variation seen in extrusive rocks is seen in intrusive rocks, but the rocks are given different names:

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none Lherzolite Ultramafic

Basalt Gabbro Mafic

Andesite Diorite Intermediate

Rhyolite Granite Felsic

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Ultramafic rocks are almost entirely ferro-magnesian minerals. Ultramafic extrusive rocks are very rare and most ultramafic rocks are the residue of partial melting.

Mafic rocks contain roughly equal amounts of ferro-magnesian minerals and calcic feldspar.

Intermediate rocks may contain minor quartz 20 to 30% ferromagnesian minerals and intermediate (Na-Ca) plagioclase feldspar.

Felsic rocks contain minor ferromagnesian minerals, abundant quartz and both Na and K feldspars.

Igneous rock compositions change as the result of partial melting and fractional crystallization. This is illustrated on "Bowens Reaction Series".

Mafic magmas are typically hotter than felsic magmas. Dissolved water greatly lowers the melting point of any magma so that a saturated felsic magma may be as low as 800 º C, whereas a dry mafic magma may be as hot as 1250 º C.

The shapes of igneous bodies also have specific names:

* A dike is a small tabular (planar) discordant body.

Here a basaltic dike intrudes precambriam sediments at Hance Rapid in the Grand Canyon, Arizona, USA.

* A sill is a small tabular concordant body

* A pluton is a large body of igneous rock that crystallized at considerable depth (>2 km).

* A stock is a small (<2) exposed pluton.

* A batholith is a large (>>100km2) exposed pluton.

Igneous bodies commonly have fine grained chilled margins and coarser-grained interiors.

We are not able to manufacture the chemical elements of the Periodic Table, so we have to go out and find them if we need them. Many of them have already been found, so we can also recycle stuff we've used previously.

Why do mineral deposits occur on Earth at all? If the Earth accreted from meteorites and the meteorites condensed from a gas phase with all of the elements mixed up together, what are the processes that concentrate similar elements to form economic deposits? For example, only one atom out of 500 million atoms in the crust is an atom of gold (Au). How, then, can nuggets of gold form that contain 1021 or 1022 (a few grams) atoms of gold?

The answer is that the igneous processes that operate on the planet set up huge distillation columns that concentrate similar elements. And the source of heat in the Earth is? . . . .  Also the weathering and transportation (erosion) processes at the surface can further concentrate some elements.

And if we understand these processes pretty well, we will know where to look for the minerals we need. Assuming we've already checked available resources from recycling.

Mineral resources are commonly divided into metals and non-metals.

Non-metals include stone, sand and gravel, cement (a major source of CO2), salt, clays, phosphate rock (fertilizer) as well as others.  Demand for non-metals is increasing.

Metals include iron (steel), aluminum, copper, zinc, manganese, lead and others. Demand for new metals derived from ore deposits is decreasing, largely due to recycling.