Working as Mineralogists

In December, students studied rocks and minerals. Students began by studying 10 minerals. They didn’t know the names of the minerals, but would analyze their characteristics, performing “tests” on them as mineralogists would, and following the tests, they would synthesize the information to determine which mineral was which.

Sophisticated, right?

Right.

One of the tests was determining the “hardness” of a mineral:

• Would my fingernail leave a scratch on it? Then it’s pretty soft.
• Would a penny leave a scratch? Still on the softer side.
• What about a nail? Now it’s getting harder.
• If none of these left a scratch, the students saw if a scratch could be made onto a piece of glass from the mineral. Some were so hard that they left a scratch on the glass!

Another test performed was the “luster” test. Did minerals have a metallic or nonmetallic luster, or shine? If nonmetallic, was the luster pearly, glassy, or some other type of luster?

A third test was the “streak” test. Students were given “streak plates” and they ran the minerals against them, seeing what color the mineral left behind. That is the true color of the mineral – if weathering had not affected it in any way.

(For example, this mineral looks grey, but when streaked, it has a reddish color.)

Students learned that they “streak” (write) with GRAPHITE every day (pencil “lead” is graphite).

Finally, students performed the “acid” test. They scraped some of the mineral into a powder, and then put a drop of vinegar on it to see if there was a reaction: Did it dissolve? bubble? Was there no reaction at all?

It was so much fun to wear goggles so that eyes were protected!

Finally, after 4 tests to analyze and time to observe the rocks closely, it was time to use the results to make a decision as to what the name of each mineral might be. Synthesizing time!

Our classroom floor was covered by students’ results books, the minerals, and the description sheets. It was exciting work. Students would make a prediction based on one test, and then look further and say, “But it has a hardness of 6-9, so it can’t be that!”

Finally, students made their most educated guesses, wondering if they were correct. It was amazing to see how many were correct…and how many were VERY close to being correct!

Congratulations, Mineralogists!