Our diamond expert says three of these are diamonds, one is not. Can you tell which is which?

GREENSBORO, NC -- A common misconception is being busted with what this Kids Want to Know! Joshua's mom sent us Joshua's Kids Want To Know question: How do diamonds form?

We went to Professor of Geology Marlene McCauley at Guilford College for the answer. But first - busting the misconception. Diamonds used to be known as nature's hardest material. Actually though, there are two minerals that are 58 percent harder than diamonds. Wurtsite boron nitride is formed during volcanic eruptions and mineral lonsdaleite is formed when meteorites containing graphite hit earth.

Now diamonds. Professor McCauley says, "First I have to start with what diamonds are. Graphite and diamond chemically are the same thing, pure carbon."

Professor McCauley says the difference is how they bond together. "When I take a hunk of graphite and I swipe it across a piece of paper like the graphite in your pencil, it makes a mark because the layers are so thin it is coming off on the sheet of paper because they are not stuck together really well. What is going to happen to this graphite if we take it deep down inside the earth? Those bonds are going to rearrange and we are going to make diamond. They stick together really well and that is what makes diamonds so hard."

So how do diamonds get it to the surface? Professor McCauley says all the diamonds that we have are very old. "All the diamonds that we mine commercially are very old and come from when the earth was quite young and were brought to the surface of the earth by extremely violent volcanic eruptions that we are very glad do not happen today."

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