Explore, Wonder, Experience our World
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The Color Test is the first and easiest test to use when identifying a rock. The color of a mineral is the first thing most people notice, but it can also be the least useful in identifying a mineral because most minerals occur in more than one color. Fluorite & quartz can be clear, white, yellow, blue, purple, or green.
Malichite is always green; azurite is always blue; and rhondonite is always red or pink. The other properties, such as hardness and luster, must be used instead. |
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Luster refers to how light is reflected from the surface of a mineral. The two main types of luster are metallic and nonmetallic. What is Metallic Luster? Minerals exhibiting metallic luster look like metal, such as a silvery appearance or that of a flat piece of steel. How many types of nonmetallic luster are there?
Another common nonmetallic luster is called translucent luster, where you can see into the mineral, but not completely through it. A mineral that displays a transparent luster transmits light completely through it, resembling glass. |
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The hardness of a mineral is its ability to resist scratching.
Where did the hardness scale originate? Friedrich Mohs, a German mineralogist, developed a hardness scale over 100 years ago. The hardest mineral known, diamond, was assigned the number 10. How does the hardness scale work? The Mohs Hardness Scale ranks the order of hardness of minerals and some common objects. For example, your fingernail can scratch the minerals talc and gypsum, with a hardness of 2 or lower. A copper penny can scratch calcite, gypsum, and talc. A common misunderstanding of how to identify a diamond is that it will scratch glass. While this is true, other minerals can scratch glass too as long as they have a hardness > 6. |
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The streak of a mineral is the color of the powder left on a streak plate (piece of unglazed porcelain) when the mineral is scraped across it. The streak plate has a hardness of glass, so minerals with a Mohs Hardness >7 will scratch the streak plate and won't powder the mineral.
Where do you observe streak? A mineral’s streak is determined by rubbing it on a streak plate, which is a piece of unglazed porcelain. The streak plate is essentially a type of glass, so it isn't used on minerals with hardness greater than 7. How useful is streak in identifying minerals? Streak can be useful for identifying metallic and earthy minerals. Nonmetallic minerals usually give a white streak because they are very light-colored. Other minerals may have very distinctive streaks. Hematite, for example, always gives a reddish-brown streak no matter what type of luster it displays. |
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Indiana’s Academic Standards for Science-2010 ~ 3rd Grade Review
Core Standard: Observe, describe and identify rocks and minerals by their specific properties. (3.2.1, 3.2.2, 3.2.3, 3.2.4)
Core Standard: Observe and describe how natural materials meet the needs of plants and animals (including humans). (3.2.5, 3.2.6)
3.2.1 Examine the physical properties of rock sample sand sort them into categories based on size using simple tools such as sieves.
3.2.2 Observe the detailed characteristics of rocks and minerals. Identify rocks as being composed of different combinations of minerals.
3.2.3 Classify and identify minerals by their physical properties of hardness, color, luster and streak.
3.2.4 Identify fossils and describe how they provide evidence about the plants and animals that lived long ago and the nature of their environment at that time.
3.2.5 Describe natural materials and give examples of how they sustain the lives of plants and animals.
3.2.6 Describe how the properties of earth materials make them useful to humans in different ways. Describe ways that humans have altered these resources to meet their needs for survival.
Core Standard: Observe, describe and identify rocks and minerals by their specific properties. (3.2.1, 3.2.2, 3.2.3, 3.2.4)
Core Standard: Observe and describe how natural materials meet the needs of plants and animals (including humans). (3.2.5, 3.2.6)
3.2.1 Examine the physical properties of rock sample sand sort them into categories based on size using simple tools such as sieves.
3.2.2 Observe the detailed characteristics of rocks and minerals. Identify rocks as being composed of different combinations of minerals.
3.2.3 Classify and identify minerals by their physical properties of hardness, color, luster and streak.
3.2.4 Identify fossils and describe how they provide evidence about the plants and animals that lived long ago and the nature of their environment at that time.
3.2.5 Describe natural materials and give examples of how they sustain the lives of plants and animals.
3.2.6 Describe how the properties of earth materials make them useful to humans in different ways. Describe ways that humans have altered these resources to meet their needs for survival.