In 2013, the Curiosity rover drilled this hole, which measures about 0.6 inches wide and 2.6 inches deep, into martian rock. The sample is now thought to contain long-chain organic molecules.

Chalk is a soft rock and wears away easily. This makes it ideal for making chalk sticks to write on blackboards. Other rocks, such as slate, do not let water soak through them. They are called ...