The strinking together of two pieces of the stone known as ______ produced spark.
Answers
Not all rocks struck together will produce a spark. In fact, most rocks will not cause a spark when struck together. The reason is because most types of rock are “softer” than others, and would not cause a spark when struck together because they would just break away. This simply results in dust particles and chips of rock.
One of the most common types of rocks actually used to start a fire is flint. You can Wikipedia what flint is. The point here is the proper characteristics of rock or stone that can start a fire. It needs to be hard enough to ensure it doesn't just “shave away” when being struck together. Of course, the cause of the spark itself is friction. And the material used needs to be able to hold together in order to cause enough friction to cause a spark, and not just be grinded down.
No matter how smooth a rock/metal is, you can cause a spark because of the microscopic unevenness on its surface. The same goes for metal. This is why “softer” rocks would just get shaved away, and harder rocks are able to rub its surface between the grooves, causing friction, and then sparks.
It's the same reason why metal being struck together is good at creating sparks. Soft metal will typically yield no sparks, just as “softer” rocks do not.
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