Minerals This study packet belongs to
What are minerals? To understand what minerals are, you need to know a bit about what makes up our Earth. Our Earth is made up of about 109 pure substances called. Elements are pure substances because all of the in that element are exactly alike. They are sort of like your fingerprints. No one else has the exact same fingerprint that you have, and no two atoms are exactly alike. So each element is unique. Let's list a few elements that you already know; This is a model of an atom showing it's parts.
Five requirements for a mineral A mineral is a combination of one or more of these elements in a specific "recipe" and arrangement. There are five requirements for a substance to be called a mineral: 1. It is not living and never was. 2. A mineral has the same chemical composition (recipe) no matter where it is found. 3. It must be a solid at normal conditions (normal temperature and pressure for our Earth's surface). 4. It must be naturally formed, not man-made. 5. Minerals will build specific shapes called crystals, even though they may to small for us to see easily with our eyes. Question - Are the minerals on our food labels the same minerals we are talking about in class? Is iron in our food the same as the iron legs of our chairs?
Scientists classify minerals by their chemical composition since it is always the same. We however cannot do that since we aren't working in a scientific laboratory. So we will investigate the physical properties of some minerals to find a way to classify them. The properties of a mineral include color, texture, crystal shape, hardness, luster, streak, magnetism, and behavior with light. We will take a look at these properties individually, and then put all of our information together to try to identify our minerals at the end of the unit. First let's start with some of the easiest observations. Find your mineral packet and label each of the pages A through L in the small boxes beside the word Mineral in the upper left-hand corner. Now take some time and draw a color sketch of the mineral you are holding, and record your observations about how it feels and smells. Remember your observations cannot be single words and need to give a clear idea. Try entries like; it smells like... one side has small ridges... it feels really heavy in my hand... this mineral has sharp edges all over... Record your observations in the three top boxes of your packet pages.
Streak test The color you see is not always considered to be the minerals true color. Some minerals come in quite a few colors. The streak test gives the minerals color by creating a powder trail on a ceramic tile. To do the streak test you just scrape the mineral on the tile until you see a mark left on the tile. It's sort of like using chalk on the sidewalk. You will do the test for each mineral on both the white and black tiles as the streak sometimes shows up better on one tile than the other, and you can compare the streaks to decide what color you are seeing. Record the results of both tests in your mineral profile packet in the Streak color box. Your observations should look like this; reddish-brown streak on white tile, reddish-brown streak on black tile Do the streak tests now.
Light tranmissivity Transmissivity means the ability to pass through. You are investigating how light passes through the mineral. You will hold your flashlight behind the mineral to see if and/or how well the light passes through the mineral. You will want to test different areas of the mineral like at the edges and in the center of the sample. You may find differences. Record all of your observations accurately. The words you will use in your observations are; opaque - no light is able to pass through translucent - some light is able to pass through transparent - almost all of the light is able to pass through Your observation might sound like; The mineral is mostly opaque except near the thinner edges where it was translucent. or The entire mineral is transparent. Assess the light transmissivity now and record your observations in the box labeled "Light" on your mineral packet.
Luster of the mineral Luster has to do with the idea of how an object looks in bright light. Think about the luster of a girl's long hair. Usually girls want their hair to be healthy, shiny, and "full of luster" like in the TV commercials. The luster of a mineral is a rating of how the mineral reflects light back to your eye. There are a few specific ratings that we will use to evaluate the luster of the mineral. This is one of the tests where you can use single words to record your observations since the words have clear meanings in our work. Be sure you know the meanings! bright metallic - looks like a metal and is highly reflective, your chair legs dull metallic - looks like a metal but is not very reflective, your desk legs earthy - nonmetallic, dull appearance, not very reflective, looks like the soil waxy - nonmetallic, sort of shiny but not really, looks like candle wax glassy - nonmetallic, looks like glass, often able to partly see through the mineral Do your luster assessment now and record your observations in the "Luster" box of your mineral profile packet.
Hardness Like we said about rocks, compared to your head they are all hard! But compared to each other, some minerals are harder than others. Back in 1812, a German mineralogist named Friedrich Mohs developed a scale for testing how hard a mineral is. It is performed by trying to scratch a softer mineral with a harder mineral or other object. He developed a ten point scale for hardness. One on the scale is very soft, and ten is the hardest. You probably know the hardest mineral on Mohs scale. The hardest mineral commonly known, #10, is (a girl's best friend). We will use a simpler version that is based upon Mohs' work, just a little easier to understand.
Hardness is really a test of how easily a mineral an be scratched by another object. You will be trying to scratch the mineral samples with a few common objects. To test the hardness of our minerals we use our thumbnail, a copper penny, and a steel nail. We will assume the mineral is soft and work our way up the hardness scale if needed. First try scratching the mineral with the softest object, your thumbnail. If the mineral is scratched by your thumbnail you are done testing that mineral. It is a very soft mineral. If the mineral is not scratched, move to the next step. Try scratching the mineral with the copper penny. If the penny scratches the mineral it is just soft, and you are done testing that mineral. If the minerals is not scratched by the penny, move to the next step. Try scratching the mineral with the steel nail. If the mineral is scratched by the steel nail, the mineral's hardness is medium, and you are done testing that mineral. If nothing has scratched the mineral so far, you are still done testing and the mineral is hard. The only ratings you will be using are very soft, soft, medium, and hard. Record your hardness observations using a phrase that tells the hardness and what scratched the mineral. Examples: medium, scratched by the steel nail or very soft, scratched by my thumbnail.
Magnetism Do you know what material is attracted to a magnet? the substance that a magnet is attracted to. This test is designed to see if there is any iron in the mineral. This is a simple test, but you still need to work carefully. Hold the mineral in your hand and bring the magnet close to the object, but don't touch the mineral. Decide whether you feel the mineral being attracted to the magnet or not. If you aren't sure, bring the magnet a little closer. Finally, touch the mineral with the magnet and see if the magnet will move the mineral or actually lift the it out of your hand. You need to choose the description that best describes how the magnet affected each mineral from the choices below. weak attraction - The magnet moved the mineral very little or seemed to affect the mineral, but it was hard to tell. strong attraction - I could really see and feel the mineral move or the magnet picked the mineral up out of my hand. no attraction - The magnet had no effect on the mineral at all. Record you observations in the "Magnetism" box of your profile packet.
Shape In this assessment, you are looking for any evidence of crystal formation. A mineral will always make crystals, and sometimes the crystals can be easily seen. But sometimes the mineral is microcrystalline, which means the crystals can only be seen using a very powerful microscope. You are to examine each mineral to see if you can see evidence of the crystal shape on the outside of the mineral, or on the inside of the mineral. You may see both. The shapes you see determine how the mineral would break if it was hit with a hammer. This quality of a mineral is called cleavage (breaks along predictable shapes) or fracture (breaks into nondistinct shapes). You should draw and describe what you see to record your observations. If you can't see any evidence of a shape or pattern in the mineral, then record "no observable shape" on your record sheet. Do not leave the "Shape" box empty.
Vocabulary to know: element atom mineral natural chemical composition luster streak transparent opaque translucent hardness crystal cleavage fracture microcrystalline