Presentation on theme: "2.2 Minerals are basic building blocks of Earth."— Presentation transcript:
12.2 Minerals are basic building blocks of Earth. A mineral is identified by its properties.
2A mineral’s appearance helps identify it. Identify a mineral by it’s properties (characteristic features)colorminerals can occur in more than one colorhow the mineral reflects light, how shiny or dull it isappearance
3Color and Streak Color Some minerals can be almost any color Most minerals have a more limited color rangeThree main factors cause minerals to vary in colorTiny amounts of an element that is not part of its normal chemical makeup.pure quartz is clear and colorless, but tiny amounts of iron can give quartz a violet color (amethyst)At or near Earth’s surface and is in contact with the atmosphere or waterDefects in crystal structures that change color
4Color and Streak Streak May have a different color when they are ground into a fine powderStreak is the color of the powder left behind when the mineral is scraped across a surface.Geologists use a tile of unglazed porcelain (streak plate), to identify mineralsBetter clue than surface color for identificationAll samples of the same mineral have the same streak.
6Luster The way light reflects from the minerals surface Metallic and nonmetallicMetallic looks as if it was made of metalNonmetallic luster can be shiny, but it does not appear to be made of metalLuster may vary from sample to sampleExposure to the atmosphere or to water can cause the surface luster to become dullIf broken its characteristic luster can be seen
8Color and Streak, Luster A mineral’s color may change when the mineral is in contact with the atmosphere or water.Minerals may get their color from small amounts of another element.The crystals of a mineral can have defects that may change their color.
9Color and Streak, Luster What is streak?A. Streak is the color of the mineral powder left behind when a mineral is scraped across a surface.What is luster?A. Luster describes the way in which light reflects from the surface.
10CleavageEach type of mineral, if hit with a hammer, will break in the same wayBetter clue to its identity than color and lusterCleavage is the tendency of a mineral to break along flat surfacesDepends on how the atoms are bondedBonds of the crystal structure are weaker in the directions in which the mineral breaksCleavage of a mineral is described by the direction in which the mineral breaks and the smoothness of the broken
11The way a mineral breaks helps identify it. Q. Why can the way a mineral breaks help identify it?A. Each kind of mineral always breaks in the same way, making it a better identifier than luster or color.
14FractureFracture is the tendency of a mineral to break into irregular piecesSome break into pieces with curved surfacesOthers may break into splinters or rough or jagged pieces.Fracture is displayed when the bonds that join the atoms are fairly equal in strength in all directions.Does not break along flat surfaces because there are no particular directions of weakness in its crystal structure.
16Fracture Why do some minerals break by fracturing? A. The bonds between the atoms of the minerals are of fairly equal strength in all directions, so there is no particular direction of weakness.
17A mineral’s density and hardness help identify it. Density is the amount of mass in a given volume of the substanceVery helpful in identifying mineralsEx. Gold and pyrite look the same but gold is much denser.Mass of gold is almost four times the mass of a piece of pyrite of the same size.Dense minerals have more mass and are heavierDetermined by the kinds of atoms that make up the mineral and how closely they are joined together.
18Hardness Hardness Harder minerals have stronger bonds A mineral’s resistance to being scratchedDetermined by its crystal structure and the strength of the bonds between its atomsHarder minerals have stronger bondsA scale known as the Mohs scale is often used to describe a mineral’s hardnessA harder mineral will scratch a softer oneTen minerals are numbered in the scale from softest to hardestTalc, the softest, has a value of 1Diamond, the hardest, has a value of 10Can only be scratched by other minerals that have the same hardness or are harderTo determine hardness, test whether it scratches or is scratched by the minerals in the scaleCan also use fingernail, a copper penny (1982 or older), and a steel file to test an unknown mineral.
19A mineral’s density and hardness help identify it. What are two properties of minerals that you could sense with your eyes closed?Density (heaviness) and hardnessWhat is density?The mass of a substance divided by its volume, it helps to describe how heavy a mineral is compared to its size.Which material would scratch the other—quartz or calcite? How do you know?A. Quartz; It has a higher value on the Mohs scale
20Hardness a mineral’s resistance to being scratched determined in part by crystal structuredetermined in part by the strength of the bonds between the atomsoften described using the Mohs scale of hardness
21Some minerals have special properties. Carbonate groupReact with acid.ChalkTested by putting a drop of a weak solution of hydrochloric acid on a sample.If CO2 gas bubbles out of the acid, then the mineral is a carbonate.FluorescenceMinerals glow when they are exposed to ultraviolet lightFluorite, calcite and willemiteLimited value in mineral identificationsamples of the same mineral may or may not display fluorescencemay glow in different colors.
22Some minerals have special properties. MagnetismA magnet is pulled toward some mineralsMagnetite strongly attracts magnetsSome other minerals weakly attract magnetsMagnets are commonly used in laboratories and industries to separate magnetic minerals from other minerals.RadioactivityAs unstable elements change into other elements over time, they release energyGeologists can measure this energy and use it to identify minerals that contain unstable elements.
24Some minerals have special properties. What are four special properties of some minerals?A.Carbonate group reacts with acid.Some minerals glow under ultraviolet light.Some minerals respond to magnets.Some minerals give off radiation.