Handbook of Nature-Study · Lesson CCXIII · Topic 33: Crystals, minerals and rocks
213. How to study minerals
Goal: Your child can test a mineral for form, color, luster and hardness, and starts a labeled rock collection.
You'll need
- A few rocks and minerals (a beginner's set from a museum shop or rock shop, plus pebbles from your yard)
- An egg carton for sorting
- A steel nail and an old plain glass bottle or small glass tile (for an adult to help with)
- A hand lens (magnifying glass)
- A nature notebook and a pencil (colored pencils if you have them)
What's in the book
This lesson is a teacher's introduction to the next five. The author tells of two small children who could pick out stones carried by glaciers, advises limiting the study to the minerals of granite and common rocks, and lists the four signs used to identify minerals: form, color, luster and hardness.
The lesson, step by step
A story to start
Read the opening story aloud. The author told two little children how certain stones near Ithaca had been carried by ice:
these stones were torn away from the mountains in Canada and brought down by ice and dropped in Ithaca.
Ask: Could some of the pebbles near us have traveled a long way too?
Gather a collection
Collect pebbles from your yard, a creek bed or a gravel driveway (ask first). If you can, get a small labeled set; the book says a teacher should have at least one. Sort them in the egg carton.
Form and color
The book's first test:
This may be crystalline, which shows the shape of the crystals definitely; granular, like marble, the grains having the internal structure, but not the external form, of crystals; compact, which is without crystalline form, as limestone or flint.
Luster
Luster or shine, which may be glassy like quartz, pearly like the inside of a shell; silky like asbestos; dull; or metallic like gold.
Sort your stones by shine. (Asbestos is harmful to breathe; a silky luster can also be seen in satin spar.)
Hardness
Easily scratched with the finger nail; cannot be scratched by the finger nail; easily scratched with steel; with difficulty scratched with steel; not to be scratched by steel.
Try the fingernail first, then the steel nail. An adult helps with the nail and any glass. If you ever break rocks with a hammer, wear safety glasses, wrap the rock in a cloth, and never hit rock on rock.
What we know now
Today rock hounds use the Mohs scale, numbered 1 (talc) to 10 (diamond). A fingernail is about 2 1/2, a steel nail or knife about 5 1/2, glass about 5 1/2, and quartz is 7. Another easy test is the streak: rub the mineral on the back of a white tile and look at the color of the powder.
Nature notebook
Start a mineral chart with columns for name (or "unknown #1"), form, color, luster and hardness. Fill in a row for three of your stones.
Afterwards
Number each stone in the egg carton and fill in its row in the chart. The next five lessons will help you name many of them.