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a Method for Identifying Metamorphic Rocks
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
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.
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?
Have students share their answers, to get them talking about the topic.
[All of this should take just a few minutes.]
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.
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.
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.
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
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
-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
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).