Part 3 Mineral properties and identifying

Properties of Minerals : 

Properties of Minerals The ways we can identify minerals

Properties of Minerals : 

Properties of Minerals Minerals occur in many different colors and shapes They also vary in how they reflect light and in how they break They vary in how hard they are They vary in smells (some stink!)

Properties of Minerals : 

Properties of Minerals Color Color is one of the first things we notice about a mineral Though in some minerals the color is unique, it is often not a useful tool in identifying a mineral

Properties of Minerals : 

Properties of Minerals Small amounts of different elements can give the same mineral different colors Below are examples of different colors of sapphires

Properties of Minerals : 

Properties of Minerals Streak This is the color of the mineral in powdered form The streak is obtained by rubbing the mineral across a streak plate, a piece of unglazed porcelain The color of a mineral may vary from sample to sample (such as sapphires), but the streak color is ALWAYS the same Because the streak is always the same, it is a good indicator to use to identify a mineral

Properties of Minerals : 

Properties of Minerals Streak The streak can also be used to see the difference between minerals with metallic lusters and minerals with nonmetallic lusters Metallic minerals generally have a dense, dark streak Minerals with nonmetallic lusters do not have such streaks

Properties of Minerals : 

Properties of Minerals Luster Luster is used to describe how light is reflected from the surface of the mineral Minerals with the appearance of metals, regardless of color, are said to have a metallic luster

Properties of Minerals : 

Properties of Minerals Metallic Luster Has the look of metal

Properties of Minerals : 

Properties of Minerals Nonmetallic Lusters These are identified by many different adjectives such as: Vitreous or glassy (quartz crystals) Vitreous is the most common nonmetallic luster Adamantine or brilliant (diamonds) Pearly (the look of a pearl) Silky (the look of silk… fibrous, but more compact) Earthy (the look of dirt and dried mud) Dull (just a non-reflective surface) Fibrous (the look of fibers)

Properties of Minerals : 

Properties of Minerals Nonmetallic Lusters More adjectives to describe the lusters Greasy (the look of grease) Gumdrop (the look of sucked on hard candy) Pitchy (the look of tar) Resinous (the look of resin or dried glue or chewing gum) Waxy (the look of wax)

Properties of Minerals : 

Properties of Minerals Crystal Form Crystal Form is the visible expression of a mineral’s internal arrangement of atoms Every mineral has a distinct crystal form When a crystal has room and time to form it will form with well formed faces (sides, top, bottom) If there is not room to grow the crystals crowd together and the crystal form is hard if not impossible to see

Properties of Minerals : 

Properties of Minerals Hardness Hardness is the measure of the resistance of a mineral to being scratched This is one of the most useful properties to use in identifying a mineral This property can be found by rubbing an unknown mineral against a mineral of known hardness Geologists use a standard hardness scale called the Moh’s Hardness Scale

Properties of Minerals : 

Properties of Minerals Moh’s Hardness Scale Consists of 10 minerals arranged from 10 (for the hardest) to 1 (for the softest)

Properties of Minerals : 

Properties of Minerals In addition to rubbing a mineral of unknown hardness against one of known hardness, other objects can be used Your fingernail (hardness 2.5) Gypsum has a hardness of 2.0 and so can be scratched by your fingernail Calcite, which resembles gypsum has a harness of 3.0 and so cannot be scratched by your fingernail A penny (hardness 3.5) A piece of glass (hardness 5.5) Diamond is the hardest mineral and can scratch anything!

Properties of Minerals : 

Properties of Minerals Cleavage Cleavage refers to the tendency of a mineral to cleave (or break) along flat, even surfaces Micas have the simplest cleavage because they have a bond in only one direction They form thin, flat sheets Silicates, such as mica, tend to cleave between the silicon-oxygen structure rather than across them Quartz has evenly strong bonds in all directions and so does not cleave, but just fractures

Properties of Minerals : 

Properties of Minerals Fracture This refers to minerals that do not show cleavage when broken Fracture is the uneven breakage of a mineral Different types of fracture Smooth, round surfaces (quartz) Called conchoidal fracture Break into splinters or fibers (asbestos) Irregular fractures

Properties of Minerals : 

Properties of Minerals Density Density is a property of ALL MATTER. It is the ratio of the objects mass to it’s volume Density can be used not only to help identify a mineral, but to determine the purity of some minerals because the density of a pure mineral is always the same

Properties of Minerals : 

Properties of Minerals Distinctive Properties Some minerals can be identified by other distinctive properties Talc and graphite are examples of using the feel of the object Metallic minerals are easily shaped Magnetite can be used to pick up paper clips Transparent Calcite acts like a magnifying glass Some streaks contain sulfur and smell like rotten eggs Carbonate minerals will fizz when they come in contact with hydrochloric acid

Properties of Minerals : 

Properties of Minerals What determines a minerals properties? A mineral’s properties depend on the elements that compose the mineral (its composition) and its structure (how its atoms are arranged)