Kiran Purohit                                                                                                        Return to Earth Science Lesson Plan Menu

Summer 2001

Devising a Method for Identifying Metamorphic Rocks

 Context & Objectives

Usually the topic of rock classification is taught as a set system with no larger purpose other than simply putting rocks into groups.  I have been thinking about the notion of classification as a method or a technique that can be used in further field work that students might be doing as part of a project, in this case a project looking at the kinds of geological resources we have in NYC, and the kinds of resources we have to bring in from outside.

 This class would come towards the beginning of a study of NYC resources, probably closely following a more general look at rock classification.  I want students to understand the geological history of the region, but also the concept that scientists use many methods for deciphering geological make-up.  This lesson, then, would be an opportunity to introduce the notion of a scientific “protocol,” a procedure that is tested and is known to work for a certain purpose.

·        Each group will develop a “protocol” for determining whether a rock sample is metamorphic, and also some possible origins for the sample.

·        We will devise as a class a list of expectations for good, useful protocols.

·        We will come up with a list of other techniques and methods that will be useful to have when doing field work in the NYC geology project.

Class Agenda

1)       Journal Question:  What do you know about metamorphic rocks?  If you could classify a certain rock formation or rock sample as metamorphic, what would be the significance of that?

2)       Pair share:  Have students share their answers, to get them talking about the topic.  [All of this should take just a few minutes.]

3)       Small Group Activity:  Give out groups of rocks, most of which are different sorts of igneous rocks.  [This group activity can either be in the form of a handout which students work through independently, or it can be more teacher-led, with more frequent “check-ins.”]

-         As a review, have students classify the rocks into igneous, sedimentary, and metamorphic.

-         Give students time, then, to classify the metamorphic rocks in some way.  They may want to come up with a table for classifying them, or devise a dichotomous key.  You can also help the whole class or a single group out by classifying another set of rocks (such as igneous) as an example.  This depends on where the students are with this work.

4)       Class Share:  Have student groups present the methods they developed and discuss them with the class.  Point out useful things that the students did not come up with.  Some of these might include:

-         The striations or layers in foliated metamorphic rock indicate ways in which it has been folded.

-         Certain kinds of crystal formations may be hints about where the rock formed.

-         The color of the rock can let you know something about its chemical make-up and what kinds of rock formed.

5)       Additional Discussion:  If you are using them, this could be a good time to introduce relevant reference tables used in earth science, such as those used for the earth science Regents exam.  This can be a good way to make sense of the context in which to use those kinds of tables.

6)       Class Discussion:  Discuss the ways in which some of the protocols people developed are better than others, and make a list of criteria that they can refer to for future protocols.  This might include a discussion of the clarity of the steps, the creation of useful keys or tables, etc.

Come up with a list of other topics which students should develop protocols about, if they are going to be doing field work (such as at Central Park and at the Palisades Interstate Park).  Some ideas might include:

-a method for finding direction

-a method for figuring out the height of a rock formation

-a method for determining crystal size or hardness of a rock, along with a calibrated scale

7)  Follow-up/Long-term Activity:  After this introduction, students would need to come up with protocols that could be discussed and shared with the rest of the class, preferably using an online discussion board where all the comments and discussion could be “public.”  These methods would then be used by other students as they design the investigations they plan to carry out on future visits to parks to do field work.  This forethought should insure that students have some investment in the work they do on these trips and take it seriously.  It also can mean that they have a better understanding of the techniques and methods they are using in their work.  At the end, ideally, these techniques can be used to answer questions students come up with about NY state/city geology, and they can present their results to the class.

 Connections to the National Standards

 This project is meant to be aligned with the National Science Education Standards’ focus on inquiry-based teaching as central to science instruction.  Therefore, this lesson is part of longer-term work in which students have a great deal of investment (Teaching Standard A).  There are ample opportunities for students to discuss their work in this lessong (Teaching Standard B), but there are also opportunities, through the later web-based work, for students who don’t catch on immediately to also participate in the work and have say.  This allows for students at different paces to work together (Teaching Standard D).