Hawai'i Space Grant Consortium, Hawai'i Institute of Geophysics and Planetology, University of Hawai'i, 1996

Edible Rocks
Teacher Page
From Exploring Meteorite Mysteries NASA EG-1997-08-104-HQ
by M. M. Lindstrom et al.
Purpose

To observe and describe physical characteristics of edible samples chosen as models of real rocks or meteorites.

Background

This activity is one of a set called Exploring Meteorite Mysteries, a teacher's guide with activities available in its entirety from NASA at: http://curator.jsc.nasa.gov/outreach/expmetmys/index.cfm (this link opens in a new window).

Meteorites are mostly pieces of rock, though a few are metal, that fall to Earth from space. Most meteorites come from the break-up of small asteroids that never accreted to form a planet. Meteorites give us clues to the origin and history of the solar system.

Meteorites come in a variety of types and a wide range of sizes and shapes, but most meteorites have two things in common: they have dark brown or black glassy crusts on the outside and contain enough iron metal to attract a magnet.

The outside crust of the meteorite is produced as the rock is heated by friction when it comes through the atmosphere. The outer part melts and forms dark fusion crust that often has flow marks or indentations like thumbprints. The inside stays cool and is usually light gray to black in color, but some may be tan or, if weathered and rusted, brown.

The simplest classification of meteorites into stony, iron, and stony-iron types is based on the amount of iron metal and silicate minerals in the meteorite. Each of the three major types of meteorites shows considerable variability and is further subdivided based on mineralogy and composition. Stony meteorites are divided into chondrites and achondrites based on whether they contain small round balls of silicate minerals called chondrules. Chondrites contain chondrules and achondrites do not. You can read more about this in the Exploring Meteorite Mysteries Teacher's guide (pdf files available).

This Activity

This activity has been designed as a comfortable introduction to describing meteorites. It helps students become better observers by making a connection between the familiar (candy bars) and the unfamiliar (meteorites).

Edible "rocks" are used in a scientific context, showing students the importance of observation, teamwork, and communication skills. Using everyday terms, students draw and describe the food.. They attempt to match their observations with short descriptions written in geologic "Field Note" style.

These six candies most closely represent meteorite characteristics:

1.
Peanut Brittle (chondrites)
2.
Rocky Road (chondrites)
3.
Thick Bar, Solid Chocolate (iron without fusion crust)
4.
3 Musketeers TM (achondrite with fusion crust)
5.
Rice Cereal Treats (meteorite regolith breccia)
6.
Chocolate brownie (carbonaceous chondrites)

Preparation

1.
Obtain the samples.
2.
Cut the samples so that a flat, cut face exposes the interior. Reserve part or most of each sample - to be eaten by the students afterwards.
3.
Place each sample in a small plastic bag. Each team of two students will have one bag containing one sample.
4.
Give one student sheet to each team.
5.
Cut apart the "Field Note" sample descriptions. These descriptions are written the way a scientist might take notes in a field record book.
6.
Arrange the "Field Note" sample descriptions on a table so that students may attempt to match their own descriptions with these "key" descriptions.
Recipes

Rocky Road

170 g (6 oz.) semi-sweet chocolate pieces; melted
120 g (2 cups) mini-marshmallows

Butter a samll pan (8 cm x 15 cm x 5 cm deep) and pour in about half of the melted chocolate. Add marshmallows and mix until coated. Pour remaining chocolate over the marshmallows and spread flat. Refrigerate until cold. Cut into small squares, so that vertical surrfaces are exposed.


Rice Cereal Treats

240 g (1/2 cup) buttor or margarine; melted
300 g (10-11 oz.) mini-marshmallows
200 g (8 cups) crispy rice cereal
170 g (6 oz.) semi-sweet chocolate pieces; melted several jelly beans, chocolate chunks, or other large edible lumps

Melt butter and marshmallows together; stir until smooth. Pour over cereal in large bowl, and stir until coated. Press half of mixture into buttered baking pan (20 cm x 25 cm x 5 cm deep) and top with layer of melted chocolate. Press remaining cereal mixture on top of the chocolate layer. When cooled but still moldable, cut one cube about 5 cm square. Cut this square again once or twice. Embed one or two jelly beans and other lumps into the cut cube. Mold these cut pieces together again to form a "breccia". Allow to harden. Recut to expose interior and jelly bean and other lumps.


Chocolate Brownies

Use any recipe for dark chocolate brownies or box mix. Add large chunks of chocolate pieces; enough so that the pieces will be exposed on a cut surface. Bake according to directions and cool completely. Cut into small squares.

In Class

Distribute a sample and student sheet to each team. Note: Content vocabulary should not be expected initially. The processes of observing and recording should be kept simple.

Explain that each team is responsible for describing and sketching its sample. Encourage teams to describe their observations using familiar vocabulary; however, use no food terms.

Emphasize that working together is important.

When finished, students should go to the "Field Note" sample descriptions which you have arranged on the "key" table. Emphasixe that their observations will not be exactly like the "Field Notes". They will likely try several matches before they have the accurate paring.

Reward the students with pieces of the reserved candies.

Wrap-Up

Have each team share their descriptions and sketches with the class. Conduct a discussion that includes the following points which emphasize basic skills needed to be good scientists:

During the discussion, you may expand and help define the meteorite and geologic vocabulary in context and encourage students to apply it to their own samples.



"Field Note" Sample Descriptions

These food descriptions are in geologic "Field Note" style. Therefore, they may be short and sometimes cryptic. Use of geologic terms will encourage students to stretch their minds.



1.
Sample is a thin layer. There is a golden matrix surrounding tan rounded or broken inclusions. The inclusions have a reddish brown rim or crust.

2.
Sample consists mainly of white, soft, rounded to angular blebs completely surrounded by a uniform dark brown matrix.

3.
Sample is a solid, dark brown, dense mass with no obvious fusion crust.

4.
Sample has a homogeneous light brown interior with a few small vesicles. The exterior looks like a fairly regular, dark brown fusion crust with some patterning.

5.
Sample appears to have been distorted. The dominant phase is made of rounded light tan fragments containing many void spaces. A dark brown thin layer fills spaces between some rounded fragments. There are some large foreign inclusions.

6.
Sample is totally dark brown with two phases. The dominant phase is shiny and crumbly. The other phase is dense and slightly lighter in color. A light fusion crust appears on only one side.


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