Characteristics of Minerals What are the identities of the unknown minerals.

  

Characteristics of Minerals What are the identities of the unknown minerals.

Lab Handout

Lab 13. Characteristics of Minerals: What Are the Identities of the Unknown Minerals?

Introduction Rocks are made up of different types of minerals or other pieces of rock, which are made of minerals. Granite (Figure L13.1) and marble (Figure L13.2) are examples of different kinds of rock. Earth scientists group rocks into one of three categories:

● Sedimentary rocks are formed at the Earth’s surface by the accumulation and cementation of fragments of sediments. Sandstone is an example of a sedimentary rock.

● Igneous rocks form through the cooling and solidification of magma or lava.Granite is an example of an igneous rock.

● Metamorphic rocks are produced when existing rocks are subjected to extreme temperature and pressure. Marble is an example of a metamorphic rock.

Earth scientists use the mineral composition of a rock to classify it. Granite, for example,is made up of minerals such as quartz, feldspar, and biotite; marble is made up of minerals called dolomite and calcite. Earth scientists must be able to determine the various types of minerals that are in a rock in order to identify it. Every mineral has a

Characteristics of Minerals What are the identities of the unknown minerals?

unique chemical composition. Dolomite (see Figure L13.3, p. 322), for example, has the chemical composition of CaMg(CO3)2, whereas quartz (see Figure L13.4, p. 322) has a chemical composition of SiO₂. The unique chemical composition of a mineral gives it a specific combination of chemical and physical properties. Earth scientists use these chemical and physical properties to identify a mineral.

Chemical properties (see Figure L13.5) describe how a mineral interacts with other types of matter. Dolomite, for example, reacts with hydrochloric acid but quartz does not. Physical properties are descriptive characteristics of a mineral. Examples of physical properties include color, density, streak (whether the mineral streaks on a streak plate and the color of the powder), hardness (whether the mineral can scratch something with a known hardness, like glass or a nail), smell, how the mineral breaks (cleavage is when a mineral breaks evenly along a flat surface; fracture is when a mineral breaks apart roughly), and luster (whether the material appears metallic or nonmetallic). Some minerals will even attract magnets.It is often challenging to determine the identity of an unknown mineral based on its chemical and physical properties. For example, if an Earth scientist has only a small amount of a mineral, he or she may not be able to conduct all

Characteristics of Minerals What are the identities of the unknown minerals?

the different types of tests that are needed because some tests may change the characteristics of the mineral during the process (such as when dolomite is mixed with an acid). It is also difficult to determine many of the physical properties of the sample, such as its density or its luster, when there is only a small amount of the substance, because taking measurements is harder. To complicate matters further, an unknown mineral may have an irregular shape, which can make it difficult to accurately measure its volume. Without knowing the mass and the volume of a substance, it is impossible to calculate its density. In this investigation, you will have an opportunity to learn about some of the challenges Earth scientists face when they need to identify an unknown mineral based on its chemical and physical properties and why it is important to make accurate measurements inside the laboratory.

Your Task

You will be given a set of known minerals. You will then document, measure, or calculate at least three different chemical or physical properties for each mineral. Then you will be given a set of unknown minerals. Your goal is to use what you know about the physical and chemical properties of matter, proportional relationships, and patterns to design and carry out an investigation that will enable you to collect the data you need to determine the identity of the unknown minerals.

The guiding question of this investigation is, What are the identities of the unknown minerals?

Materials You may use any of the following materials during your investigation:

● Gizmo Mineral Identification Simulation

● Known Mineral Samples Sheet G-I

● Unknown Mineral Samples J-L (located on the Gizmo Simulation: Mineral

Identification)

● Mineral Identification Key

Safety Precautions Follow all normal lab safety rules.

Investigation Proposal Required? (Highlight one) Yes No

Characteristics of Minerals What are the identities of the unknown minerals?

Getting Started To answer the guiding question, you will need to make several systematic observations of the known and unknown minerals. To accomplish this task, you must determine what type of data you need to collect, how you will collect it, and how you will analyze it.

To determine what type of data you need to collect, think about the following questions:

● Which three properties will you focus on as you make your systematic observations? The properties you choose to focus on can be chemical ones (reactions with other substances) or physical ones (e.g., color, density, hardness, streak).

● What information do you need to determine or calculate each of the chemical or physical properties?

● How will you determine if the physical properties of the various objects are the same or different?

To determine how you will collect the data, think about the following questions: ● What equipment will you need to collect the data you need?

● How will you make sure that your data are of high quality (i.e., how will you reduce error)? How will you keep track of and organize the data you collect?

● How might the unique chemical composition of a mineral (structure) be related to its unique chemical and physical properties (function)?

● What types of patterns might you look for as you analyze your data?

● What type of calculations will you need to make?

● What type of table or graph could you create to help make sense of your data?

Connections to the Nature of Scientific Knowledge and Scientific Inquiry As you work through your investigation, be sure to think about the difference between data and evidence in science, and how scientists use different types of methods to answer different types of

questions.

Characteristics of Minerals What are the identities of the unknown minerals?

Initial Argument Once your group has finished collecting and analyzing your data, your group will need to develop an initial argument. Your initial argument needs to include a claim, evidence to support your claim, and a justification of the evidence. The claim is your group’s answer to the guiding question. The evidence is an analysis and interpretation of your data. Finally, the justification of the evidence is why your group thinks the evidence matters. The justification of the evidence is important because scientists can use different kinds of evidence to support their claims. Your group will create your initial argument on a whiteboard. Your whiteboard should include all the information shown in Figure L13.6.

Argumentation Session The argumentation session allows all of the groups to share their arguments. One or two members of each group will stay at the lab station to share that group’s argument, while the other members of the group go to the other lab stations to listen to and critique the other arguments. This is similar to what scientists do when they propose, support, evaluate,and refine new ideas during a poster session at a conference. If you are presenting your group’s argument, your goal is to share your ideas and answer questions. You should also keep a record of the critiques and suggestions made by your classmates so you can use this feedback to make your initial argument stronger. You can keep track of specific critiques and suggestions for improvement that your classmates mention in the space below.

Characteristics of Minerals What are the identities of the unknown minerals?