Minerals

Why should we care? Nearly all manufactured products we use are obtained from minerals. è aluminum: soft drink cans è graphite (carbon): our pencil lead è copper: wire for our electricity è talc: baby powder è silver & gold: our jewelry è silicon: our computer chips

Important geologic events that affect us involves rocks and minerals. è volcanic eruptions è earthquakes è weathering and erosion è mountain building

We know what a MINERAL is, but what is a ROCK? 2) contains a mixture of one or more minerals; and 3) occurs naturally as part of our planet. A ROCK: 1) is solid;

rock minerals mineral

Example From Textbook: Figure 2.2 Granite & constituent minerals

So far we have:rock collection of one or more minerals mineral A collection of one or more types of atoms minerals

Mineral Properties Each and every mineral has certain mineral properties. The properties of each mineral depends on the following:  1) The type of elements present (i.e. composition) 2) The arrangement of atoms (i.e. structure) 3) The strength of bonding (i.e. ionic, covalent (molecular), or metallic) Reference: Tarbuck and Lutgens Pages

Note - Bonding How do different atoms combine?Bonding 3 Main Ways: “ionic bond” – lose or gain electrons to form ions. Positive ions (cations) attract negative ions (anions). “covalent bond” - sharing electrons. “metallic bond” - electrons are free to move about from atom to atom.

Halite Halite (Rock Salt) is brittle in nature due to the ionic bonding between the sodium and chloride ions.

Speaking of Atomic Arrangement (Structure) Consider diamond versus graphite! Note that completely different minerals can form from the same atom, depending on how the atoms are arranged. ↑ pressure = closer packing of atoms = different substance. Temperature and pressure conditions under which minerals form are very important.

Diamond Versus Graphite Diamond and graphite are polymorphs of the element carbon; however, they differ in terms of the mineral properties hardness and cleavage due to arrangement of the carbon atoms. Diamond is hard and has no cleavage since the carbon atoms are arranged in a network covalent structure. This does not allow for any weak planes of bonding. Graphite is soft and has perfect basal cleavage (sheets) since the carbon atoms are arranged in planes of strong bonding with planes of weak bonding in between.

Diamond: Forms deep in Earth at high pressures Pure Carbon Hardest substance known to humans Crystal structure: dense and compact Graphite: Soft gray material Used as pencil lead lubricant Crystal structure: sheets of pure carbon

Quartz Versus Mica Quartz and mica could also be compared and contrasted. They compare in that both are comprised of the silicon-oxygen tetrahedron. They contrast in that quartz exhibits fracture and mica exhibits basal cleavage. I.E. Structure and Bonding

Mineral Properties The following are a list of physical properties that minerals could display:  1) Specific Gravity 2) Hardness 3) Cleavage Versus Fracture 4) Streak 5) Luster 6) Colour 7) OthersTaste, Feel, Magnetism, Acid Test, Crystal Form, Smell, Double Refraction, Tenacity, and Fluorescence.

Specific Gravity Specific Gravity (SG) is the mass of a mineral compared to that of an equal volume of water.  Weigh the specimen in air and record the weight. 1) To determine specific gravity, you need to carry out the following three steps:

Specific Gravity Weigh the specimen submerged in water and record the weight. 2)

Specific Gravity Specific Gravity = weight in air. weight in air - weight in water Calculate specific gravity (SG) using the following formula: 3) Note that if a cubic centimeter of a mineral weighs three times as much as a cubic centimeter of water, then its specific gravity is 3. With a little practice, you can estimate the SG of minerals by “hefting” them in your hand.

Specific Gravity = Density Note: (In Reference to Core Lab #3) Because pure water at 4ºC has a density of 1 g/cm 3, the specific gravity is equal to its density. Thus, Specific gravity = Density. Specific gravity has no units (it is simply a number), whereas density has units (i.e. g/cm 3 ). Density = Mass (mineral) Volume (mineral) To determine density you need to: 1) Use a scale to measure the mass of the mineral sample. 2) Find the volume of the mineral sample. 3) Calculate density (which equals specific gravity). = Specific Gravity

Specific Gravity Given: 1mL = 1cm 3 = 1g, we know the weight of an equal volume of water in grams. We can then use the following formula to calculate specific gravity: Calculation S.G. = W(mineral) W(water)

Other Properties These properties can be helpful to identify minerals that are similar: Feel - What the mineral feels like! Example: Graphite – greasy Example: Talc - soapy Taste - What the actual mineral tastes like! Example: Halite (rock salt) tastes salty.

Other Properties These properties can be helpful to identify minerals that are similar: Acid Test - Drop acid on the sample to see if the mineral reacts (i.e. fizzes). This test is used to test the carbonate group. Example: Calcite (which makes up the rocks limestone and marble). Magnetism - If a mineral is magnetic or not! Example: Magnetite (Loadstone) will attract metal objects.

Other Properties Smell: The mineral sulfur smells like rotten eggs.

Other Properties Double Refraction: This is an optical property. For example, when a transparent piece of calcite is placed over printed material, the letters appear double.

Other Properties Tenacity: Mica (muscovite and biotite) will bend and elastically snap back. Gold is malleable, which means that it can be hammered into sheets.

Other Properties Crystal Form (Shape): Already completed in the notes.

Crystal Form - Remember Shape or form of a crystal can reflect the orderly internal arrangement of atoms. Example: Quartz (SiO2)

Crystal Faces The smooth flat surfaces on crystals are called faces.

Other Properties Fluorescence: When light from a source strikes a mineral and reacts with the component chemicals, thereby making the mineral glow. Example: Gypsum

Sample Problem Explain how the specific gravity of a mineral is determined. Answer: Specific gravity compares the weight of a mineral to the weight of an equal volume of H 2 O. (i)Find the mass of the mineral; using a scale or balance. (ii)Find the volume of the mineral; using the water displacement method. (iii)Find the weight of the mineral in water; by suspending the mineral from the spring scale and weighing it immersed in water. (iv)Use the formula; S.G. = density = m/v OR S.G. = (weight of mineral in air) (weight in air) - (weight in H 2 O)