How the "Become a Rock Detective" Program Works
Try Solving This Mystery! 
(See Answer Sheet for the "Oh, Wow!")

Diatomite

SEM Image

Scanning Electron Image of Diatom



The "Oh, Wow!" in this Mystery is about a rock (called diatomite) made of plant fossils shaped like tiny, tiny soda straws!

See the Answer Sheet (below)


 
ANSWER SHEET
#15

MYSTERY SAMPLE:

- A piece of Diatomite.

OBJECTIVE:
- To introduce diatomite, diatoms, and the concept of a rock made of diatom shells or tests
- To introduce the idea that a rock can be made of little hollow things
- To introduce the concept of the elemental composition of minerals

ANSWER:
- I am light because I am made of billions of hollow shells filled with air. 

TEACHING TECHNIQUES FOR 'STAFF MEETING:'
- Hold up the sample and ask why it is so light. Get many ideas and write them on the board. You want the little detectives to 'discover' that the rock is made of hollow shells of diatoms shaped like soda straws. Diatoms are one-celled plants that appeared in the geologic record in the Cretaceous (approximately 100 million years ago). They are very common today, and are responsible for the red or green color of water in lakes, rivers, bays, and the ocean.
- Now, you can explain that in the United States, a famous kind of diatomite rock is found in Nevada. It formed millions of years ago in a huge fresh water lake when billions and billions of the little plants died and their tests (shells) sank to the bottom. The resulting bed, or rock strata, is many feet thick because the diatoms lived and died in this huge lake for many, many, many years.
- Diatomite, which is NOT chalk, is composed of silica and oxygen (SiO2), the same material that is used to make window glass. Diatomite will not fizz when you put a little dilute acid on it. However, chalk will fizz because it is made of tiny animal shells composed of calcite (CaCO3) that release carbon dioxide (CO2).
- Dynamite was once made with diatomite! Today it is used to insulate steam pipes because it doesn't conduct heat very well.

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