Here's why:

* Sedimentary rocks are formed from the accumulation and cementation of sediments like sand, mud, or shells.

* Metamorphic rocks form when existing rocks (igneous, sedimentary, or even other metamorphic rocks) are transformed by heat, pressure, or chemical reactions.

Tiger's eye is formed when crocidolite, a type of fibrous blue asbestos, undergoes metamorphism. The fibers within the crocidolite become coated with silica, which gives the stone its distinctive chatoyancy (the shimmering effect you see).