Which of the following is not one of the three types of rocks?

The choice of "Elastic" as the answer is correct because it does not represent a category of rock formation. The three recognized types of rocks in geology are metamorphic, igneous, and sedimentary.

Metamorphic rocks form from the alteration of existing rock types due to heat, pressure, or chemically active fluids, leading to changes in mineral composition and texture.

Igneous rocks originate from the solidification of molten material called magma or lava. They can be further classified into intrusive (formed beneath the Earth’s surface) and extrusive (formed on the surface) varieties.

Sedimentary rocks are formed through the accumulation and compaction of mineral and organic particles, often in layers, and can include features such as fossils.

Elastic, while it may refer to a property of certain materials, is not a classification in the context of rock types, making it the option that does not belong in the list.