It's impossible to definitively say what type of rock it is based solely on its color. Many rocks can be tan and dirty white, so you need more information to narrow it down.

Here are some questions to consider:

* Where did you find the rock? Location can help. For example, a rock found on a beach is likely different from one found in a mountain range.

* What is the rock's texture? Is it smooth, rough, or bumpy? Does it have any crystals or grains visible?

* Does it have any other identifying features? For example, does it have any streaks of color, fossils, or unique patterns?

Once you have a better description, you can use a rock identification guide or website to help you determine the type of rock.

Here are some possibilities based on your description:

* Sandstone: This sedimentary rock is often tan or white, depending on the sand grains that make it up. It can be smooth or rough depending on how it was formed.

* Limestone: Another sedimentary rock, limestone can be white, tan, or even gray. It can be quite smooth, particularly if it has been polished by water.

* Marble: This metamorphic rock is often white or tan and can have a smooth, polished surface.

* Quartzite: A metamorphic rock formed from sandstone, quartzite can be tan, white, or even pink. It can be smooth or have a somewhat gritty texture.

Remember, without more information, it's hard to say for sure what type of rock you have.