Defining the Atom • Atomic Theory • All matter is made up of very tiny particles called atoms • Atoms of the SAME element are chemically alike • The atoms of an element have a definite mass that is characteristic of the element • The Atoms of different elements have a different number of protons in their nucleus (so atoms of different elements have different atomic masses). • Atoms are not subdivided, created, or destroyed in chemical reactions • Sizes of Atoms: Atomic Radius • Atoms are about 1 X 10-12 m in size…so cannot be seen (why we call it the atomic “theory”)
What makes elements different? • What is an element? • The atoms of different elements have a different number of protons in their nucleus • An element is a substance that cannot be broken down to any simpler substance; made up of all the same atoms each with the same number of protons in the nucleus • Examples: Hydrogen has just one proton in it’s nucleus, Lithium has 3; Berillium has 4; Sodium has 11. • The number of protons in the nucleus is called the atomic number!
Structure of the Atom • Structure of the Atom: • All atoms are composed of subatomic particles called electrons, protons, and neutrons • Electrons, protons, and neutrons are different in terms of their mass, electrical charge, and location in the atom • Protons and neutrons have the same mass, while electrons are much lighter. • Protons have a positive charge, neutrons are neutral (no charge) and electrons have a negative charge • Protons and neutrons are found in the center of an atom (nucleus), while electrons are attracted to the protons on the outside of the nucleus (opposite charges attract)
I. Minerals • All minerals are made up of single elements or compounds. • Element = a substance that cannot be broken down to any simpler substance; made up of atoms • Atom = smallest part of an element; has all the properties the element has but cannot be seen even with tools • Compound = substances consisting of more than one element
Minerals - definition • Naturally Occurring • synthetic substances are not minerals • Inorganic • plant and animal activities (coal, pearls are not minerals) • Solids • Definite Chemical Composition • Crystalline Structure • a crystal is a regular geometric solid shape; reflects the ordered internal arrangement of atoms • Definite Set of Physical Properties
Physical Properties of Minerals • Can be used to identify minerals! • Color • Luster • Streak • Odor • Hardness • Breakage Pattern • Cleavage • Fracture
Color Very useful property only for some minerals Not useful for other minerals because: 1. Many minerals come in multiple colors 2. One color (such as white) can be seen in many minerals May be used for some of the obvious minerals that are almost always one color (sulfur = yellow)
Is color always a useful physical property for identifying minerals? • NO! • But it sure makes looking at minerals a lot more interesting!
Luster... • The way light shines or glares off the surface of minerals • Better than color to identify minerals • Many types of luster have been described • Somewhat subjective • Need to familiarize yourself with terms...
Luster... • Metallic • looks like metal in the way the mineral reflects light (Galena or Pyrite) • Non-Metallic • Does not look like polished metal, so other terms are used.
Types of Non-Metallic Luster • Vitreous - glassy, like glass (quartz) • Resinous - a dull shine, like a resin (amber, olivine) • Waxy - dull shine like candle wax (sulfur, olivine) • Adamantine - brilliant glow, beam of light at a certain angle (diamond) • Earthy - no shine at all (bauxite) • Pearly - looks like pearls when light is reflected off the minerals surface (opal, garnet)
The way light reflects off the surface of a mineral (luster) is useful in identifying the mineral
Galena definitely has a metallic luster as it looks like polished metal Graphite may display a “sub-metallic” luster, as it looks like dull metal Quartz has a glassy look, which is called a “vitreous” luster
Match the luster description with the appropriate luster term by writing the correct number next to the term:
Streak • The color of the powder of a mineral obtained by rubbing the sample across an unglazed porcelain plate (called a streak plate) • Most minerals display only one color of streak • Examples: • Hematite always has a reddish brown streak, no matter what color the sample is • Sulfur has a yellow streak • Sphalerite has a yellow streak • Magnetite has a black streak
When checking the streak of a mineral, be sure to follow these steps: • Hold streak plate carefully with index finger and thumb of one hand • Hold streak plate firmly against desk top • Rub mineral across plate firmly to powder it
Checking streak... • Be careful not to break off the corners of the streak plate. • Some streak plates have sharp edges so WATCH OUT! • Check the color of the minerals powder to determine streak.
Color, Luster, and Streak Quiz! • Color is the most useful property used to identify a mineral. • FALSE! Too many minerals are the same color and many are white, green, black, etc.
Color, Luster, and Streak Quiz! • Vitreous is a type of non-metallic luster seen on minerals that reflect light as glass does. • True! Vitreous is glassy.
Color, Luster, and Streak Quiz! • The way a mineral reflects light is called streak. • FALSE! Luster is the way a mineral reflects light. Streak is the color of the mineral in powder form.
Color, Luster, and Streak Quiz! • Determining the streak of a mineral is done by whacking the mineral with a sledge hammer until it is pulverized. • FALSE! Streak is easily determined by rubbing the mineral across an unglazed porcelain plate.
Color, Luster, and Streak Quiz! • The streak of a mineral will always be the same as the mineral color. • FALSE! Streak is particularly useful when it is different than the color of the mineral itself.
Hardness of Minerals • Hardness is the resistance of a mineral to being scratched • All minerals are assigned a hardness value from 1 – 10 based upon “Moh’s Hardness Scale” • Hardness is one of the most useful properties because: • Resistance of a mineral to being scratched never changes among different samples of the same mineral • Hardness is easily determined using your fingernail, a glass plate, a steel nail, and reference minerals
Hardness = the resistance of a mineral to being scratched • Mineral Name (Moh’s Scale)Typical Uses • 1. Talc body powder • 2. Gypsum building (wallboard, etc.) * 2.5 Human Fingernail • 3. Calcite lenses in microscopes • 4. Fluorite toothpaste • 5. Apatite fertilizer * 5.5 GLASS PLATE • 6. Feldspar floor tiles (mall floors) • 7. Quartz watches, abrasives, etc. • 8. Topaz gemstones • 9. Corundum abrasives, cutting tools • 10. Diamond saws, “a girl’s best friend”
Diamonds are so prized because they are harder than any other substance, so they are extremely resistant!
Diamond particles that are not used as gemstones can be used in cutting saws, and are able to cut all other industrial materials.
Hardness - continued… • Hardness is a very useful property, since a mineral’s hardness is constant – it is the main way we can separate “soft” minerals (1-5 on Moh’s scale) from “hard” minerals (6-10) • “Hard” minerals such as quartz are used as abrasives • Fingernail is a 2.5 on Moh’s scale, so can be used to identify very soft minerals (scratched by fingernail) • Steel nail is about 5.0 on Moh’s scale • (softer than glass)
Hardness... • How do we determine the hardness of a mineral? • First, we rub an edge of the mineral across a glass plate, to see if it scratches the glass. Remember, a glass plate is about 5.5 on Moh’s hardness scale. • Once we determine whether the mineral is harder (scratches) or softer (does not scratch) than 5.5, we use the reference minerals of Moh’s hardness scale and other items such as our fingernail, steel nail, etc. to more accurately determine hardness.
Checking for Hardness... • Be sure to hold the glass plate down firmly on the desk • Be careful of sharp edges on the glass plate! • Glass can be very fragile and sharp! • Wipe mineral across glass plate to see if it scratches the glass
Checking hardness... • Check to see if the mineral actually made a groove in the glass or just merely rubbed off on the glass • A mineral is harder than glass if there is a definite groove or scratch in the glass plate.
Hardness of Minerals… • If the mineral does not scratch glass (less than 5.5), try to scratch it with your fingernail • If your fingernail can scratch the mineral, it is also less than 2.5 on Moh’s scale • If your fingernail does not scratch the mineral, it is between 2.5 and 5.0 on Moh’s scale. • KNOWING THE HARDNESS VALUE WILL MAKE IDENTIFYING THE MINERAL MUCH EASIER!!!!
Breakage Pattern • 1. Cleavage - the tendency of a mineral to split consistently along certain planes of weakness • 2. Fracture - no definite planes of weakness so mineral just breaks along irregular surfaces
Cleavage... • Minerals may show one or more planes of weakness: • one plane of weakness = basal (muscovite mica) • two planes of cleavage at 90º (orthoclase) • three planes of weakness at 90º = cubic (halite) • three planes not at 90 º = rhombohedral (calcite) • You must look carefully for “flat” surfaces which give off a glare to find the cleavage in a mineral • Not always obvious
Cleavage... • Some minerals such as mica break apart along one smooth flat plane, called BASAL cleavage. • This sample has also been cut into straight edges.
Cleavage... Basal cleavage (muscovite mica) 2 directions of cleavage at 90º (feldspar) Cubic cleavage (galena)
Fracture... • Conchoidal fracture - irregular breakage surfaces are somewhat rounded (like the way glass breaks) • Quartz is noted for its conchoidal fracture • Hackly fracture - breakage surfaces are jagged (such as the mineral copper) • Uneven fracture - some minerals break apart in no distinguishable pattern.
Fracture... Hackly fracture (copper) Conchoidal fracture (Quartz)
Quiz… • Minerals are mostly man-made. • False. Minerals are naturally-occurring.
Quiz... • Minerals usually exhibit a characteristic streak, or powder color. • True.
Quiz... • Moh’s hardness scale is used to determine a mineral’s luster. • False! Moh’s scale is used to determine hardness.