Scripture: Genesis 27-28
- Students will review the story of Jacob’s blessing and dream, focusing on the idea Jacob used a rock for a pillow.
- Students will learn people in ancient times often used hard objects for pillows.
- Students will learn that different rocks have different amounts of hardness and knowing how hard a rock is can help you identify a rock.
- Students will learn about the Mohs test for determining the hardness of rocks and minerals.
- Students will participate in an activity to help them practice testing the hardness of various rocks and minerals.
Guiding Question: How can we determine how hard a rock is?
Materials: various samples of different rocks and minerals, pennies, stainless steel spoons
Procedure: Review the story of Jacob focusing on the idea of Jacob using a rock as a pillow. Explain to students that people in ancient times often used hard items as pillows. Tell students that even though as a pillow all rocks probably feel equally hard, some rocks are actually harder than others. Explain the Mohs scale of hardness to students (Softest – Talc=1, Gypsum=2, Calcite=3, Fluorite=4, Apatite=5, Orthoclase=6, Quartz=7, Topaz=8, Corundum=9 and Diamond=10 – hardest). Explain to the students that if they are given some mystery rocks and minerals testing them for hardness can help them identify the rock or mineral. For example if a rock tests a 1, then it is definitely not quartz or a diamond, but is most likely Talc or something very similar to Talc.
Have students use their fingernails (Mohs 2.5), a penny (Mohs 3) or stainless steel spoon (Mohs 5.5) to try and determine where the mystery stones might fall on the hardness scale. If an object of known hardness makes a “scratch” in a rock, the rock is softer than that hardness. If you identify one of the rocks – quartz – for example, can they identify the rocks even more closely?
- What Mohs measurements do other rocks and minerals have besides the ones listed on the scale?
Supplemental Activity: Have more advanced students research and find the Mohs numbers for other common rocks and minerals. Have them repeat the activity and see if they can more accurately identify the mystery rocks and minerals.