Earth Science: Minerals: Identification and Properties
Using observable properties to identify common minerals
Earth Science: Minerals: Identification and Properties
Using observable properties to identify common minerals
Earth Science - Grade 6-8
- 1
A sample is naturally occurring, inorganic, solid, has a definite chemical composition, and has atoms arranged in a crystal structure. Does it meet the scientific definition of a mineral? Explain.
Check the sample against each part of the mineral definition.
Yes, it meets the scientific definition of a mineral because it has all five required characteristics: it is naturally occurring, inorganic, solid, has a definite chemical composition, and has a crystal structure. - 2
A student finds a shiny yellow material in a stream. It looks like gold, but it can be scratched by a copper penny. Gold has a hardness of about 2.5 to 3, and pyrite has a hardness of about 6 to 6.5. Is the sample more likely to be gold or pyrite? Explain.
A copper penny has a hardness of about 3 on the Mohs scale.
The sample is more likely to be gold because it can be scratched by a copper penny, which means it is softer than copper. Pyrite is much harder and would not be scratched easily by a penny. - 3
Why is color usually not the best property to use by itself when identifying a mineral?
Color is usually not the best property to use by itself because many minerals can have different colors due to impurities, and different minerals can have the same color. - 4
A mineral is rubbed across a white streak plate and leaves a reddish-brown powder. What property is being tested, and why can this be more useful than the mineral's outside color?
Streak is the color of a mineral's powder.
The property being tested is streak. Streak can be more useful than outside color because it shows the color of the mineral in powdered form, which is often more consistent than the surface color. - 5
A mineral reflects light like metal. Another mineral reflects light like glass. Name the property being described and identify the two types of this property.
The property being described is luster. The first mineral has metallic luster, and the second mineral has nonmetallic or glassy luster. - 6
A mineral breaks along flat, smooth surfaces in three directions. Is this cleavage or fracture? Explain how you know.
Cleavage means a mineral breaks along repeating planes of weakness.
This is cleavage because the mineral breaks along flat, smooth planes. Fracture would break in uneven, curved, or rough surfaces instead. - 7
A mineral has a mass of 48 grams and a volume of 16 cubic centimeters. Calculate its density.
Use the formula density = mass ÷ volume.
The density is 3 grams per cubic centimeter because density equals mass divided by volume, and 48 grams divided by 16 cubic centimeters equals 3 grams per cubic centimeter. - 8
Two minerals are the same size, but Mineral A feels much heavier than Mineral B. What physical property is different, and how could you measure it more accurately?
The physical property that is different is density. You could measure it more accurately by finding each mineral's mass with a balance, finding its volume, and calculating density using mass divided by volume. - 9
Use these clues to identify the mineral: it is very soft, can be scratched with a fingernail, feels slippery or soapy, and has a hardness of 1 on the Mohs scale.
Talc is the softest mineral on the Mohs hardness scale.
The mineral is most likely talc because talc has a hardness of 1, can be scratched with a fingernail, and often feels slippery or soapy. - 10
Use these clues to identify the mineral: it has a salty taste, forms cube-shaped crystals, and has cubic cleavage. In a school lab, you should not taste unknown minerals. What is the mineral likely to be?
The mineral is likely halite because halite has a salty taste and commonly forms cube-shaped crystals with cubic cleavage. - 11
A mineral sample fizzes when a drop of weak acid is placed on it. Which common mineral is most likely present, and what property is being tested?
Calcite reacts with weak acid because it contains carbonate.
The mineral is most likely calcite. The property being tested is its chemical reaction with weak acid, which produces fizzing. - 12
A black mineral is attracted to a magnet and leaves a black streak. Which mineral is the best match: quartz, magnetite, or gypsum? Explain.
The best match is magnetite because magnetite is magnetic and commonly has a black streak. Quartz and gypsum are not strongly attracted to magnets. - 13
A student uses the following data for an unknown mineral: hardness 7, glassy luster, no cleavage, curved fracture, and white streak. Which mineral is a strong match: quartz, mica, or talc? Explain.
Quartz commonly breaks with conchoidal, or curved, fracture.
Quartz is a strong match because it has a hardness of 7, glassy luster, no cleavage, curved fracture, and a white streak. Mica has cleavage, and talc is much softer. - 14
Mica can be peeled into very thin sheets. Which property does this show, and what does it tell you about the arrangement of mica's atoms?
Think about how the mineral breaks, not just how it looks.
This shows cleavage in one direction. It tells us that mica's atoms are arranged so the mineral has weak planes where it can split into thin sheets. - 15
You are given an unknown mineral. List four tests or observations you could use to identify it, and explain why using several properties is better than using only one.
Four useful tests or observations are hardness, streak, luster, and cleavage or fracture. Using several properties is better because one property, such as color, may be shared by many minerals or may vary within the same mineral.