There isn't a single, definitive answer to how many different types of rocks are in the world. It depends on how you define "type."

Here's why it's tricky:

* Classification: Rocks are classified into three main categories: igneous, sedimentary, and metamorphic. Within each category, there are numerous subcategories.

* Variations: Even within the same rock type, there can be significant variations in mineral composition, texture, and color. These variations can be subtle or dramatic, making it difficult to draw a clear line between "types."

* New discoveries: Geologists are constantly discovering new rock formations and variations, so the number is constantly evolving.

Instead of a precise number, here are some ways to think about the variety of rocks:

* Hundreds of recognized rock types: There are hundreds of officially recognized and named rock types, with new ones being added regularly.

* Countless variations: The number of unique variations within these rock types is practically immeasurable.

To put it simply, the world is filled with an astounding diversity of rocks, and the number is constantly growing!