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It’s red. It’s a truck. But it’s not a FIRE truck. More important than the red color are features like hoses, ladders, sirens, flashing lights, axes, and guys (or gals) in rubber boots and strange hats. A dalmatian can be a pretty good clue as well. And if you find a red truck in a fire house, that's a dead give-away. This truck lacks all those features, so it's not a fire truck
Red truck again. But still a long, long way from a FIRE truck. It could be a municipal vehicle, and it could have guys (or gals) in boots and strange hats. But still no hoses or ladders, and the load of trash is highly uncharacteristic of a fire truck.
Here we go! It’s red and it’s a truck But it has also got: hoses sirens ladders a nice sign on the door that says "Fire Dept." I realize that to anyone even vaguely exposed to modern society, this is obviously a fire truck. You don't think about it, you just look at it and know. However, a whole series of visual clues (or properties) are being processed by the brain to make this determination. Even though you probably don't even realize that you are processing any clues, you are doing it on a subconscious level.
Still a fire truck? Of course. It still has got: hoses sirens ladders a nice sign on the door that says "Fire Dept." You can still do a heck of a job putting out fires with it. So, fire truck ID is about the features. and...wait...the same is true for minerals? yeah, we’ll get there in a minute
Still a fire truck? Of course. Color is not diagnostic for fire trucks.(or for minerals either) Let’s rephrase that a bit, color can be an important tool for identifying things, but it's not conclusive. Check the other properties, they have to be right.
So what is a mineral?What are the characteristics of all minerals?
Of the almost 4000 known minerals, only about 30 are common. The most common are quartz, feldspar, mica, and calcite.
These minerals make up most of the rocks found in the Earth’s crust.
In fact, over 60% of the Earth’s crust is made up of the family of minerals known as feldspar!
Identifying Minerals Remember!: Rarely is a mineral identified by a single property. These properties need to be considered together.
Color Color is the most easily observed mineral property and the least useful!
Color Many minerals have a similar color.
Color Many individual minerals (quartz, calcite, etc…) come in different colors.
Color For example, pure quartz is colorless or white, impurities can make the mineral rose, purple or pink!
luster Lusterrefers to the way a mineral shines in reflected light. Notice the difference between these two minerals?
luster Metallic luster is very shiny, nonmetallic luster is very dull.
Streak Streak of a mineral is the color of its powder when rubbed on white tile.
Streak The streak is often not the same color as the mineral. A minerals color may vary, but the streak rarely will!
Cleavage The cleavageof a mineral is its tendency to split easily or to separate along flat surfaces.
Cleavage Mica is probably the best example as it splits into thin sheets. It is said to have one perfect cleavage.
Cleavage Feldspar splits readily in two directions, always at or near right angles.
Cleavage Calcite and galena cleave in three directions. They are said to have three good cleavage directions.
Cleavage Not all minerals show cleavage. Those that don’t break along cleavage surfaces are said to have fracture.
Hardness The hardnessof a mineral is its resistance to being scratched. Diamond is the hardest of all minerals, and talc is the softest.
Hardness Friedrich Mohs devised a hardness scale. In this scale, ten well known minerals are given numbers from one to ten. Lets take a look at the ten minerals used and some of the simple tests.
Hardness Talc (left) is the softest and has a hardness of 1. A soft pencil lead will scratch talc. Gypsum is a bit harder and has a hardness of 2. A fingernail scratches gypsum.
Hardness Calcite (left) has a hardness of 3 and a copper penny just scratches it. Fluorite has a hardness of 4 and it can be scratched by an iron or brass nail.
Hardness Apatite (left) has a hardness of 5 and can be scratched by a steel knife blade. Feldsparhas a hardness of 6 and it will scratch a window glass.
Hardness Quartz (left), with a hardness of 7, is the hardest of the common minerals. It easily scratches hard glass and steel. Topaz has a hardness of 8 and will scratch quartz.
Hardness Corundum (left) has a hardness of 9. Corundum will scratch topaz. Diamond with its hardness of 10 can easily scratch the rest of the minerals.
Discuss the following! Does this mineral show cleavage or fracture?
crystal shapes Crystal shape can be a useful property to identify minerals.
Density Density is mass per unit volume Pure gold is very dense
acid test Calcite is calcium carbonate, CaCO3. If a drop of weak hydrochloric acid is placed on calcite, the acid bubbles as carbon dioxide is released.
Other Special Properties Magnetic Malleable Radioactive Flourescence Taste
Magnetic Some minerals that contain Iron, are magnetic and can be picked up by a magnet.
Taste Halite (rock salt) can be identified by its taste. This practice is not recommended!
