If you picked up a basalt rock which was shaped like a teardrop it could be a

Volcanic bomb

Explanation:

Volcanic bombs are the extrusive igneous rocks that are produced when the magma erupts on the surface with greater force. These are larger in size, they have a diameter of more than 64 mm. The shape of this volcanic bombs resembles a teardrop, which is shaped during its time of eruption as it is on the flight. During the time of the eruption, these rocks are viscous in nature and it cools down subsequently, it becomes hard and solid.

Thus, the correct answer is a volcanic bomb.