Here's why:

* Sandstone is formed from sand. Sandstone is a sedimentary rock, meaning it's formed from the accumulation and cementation of smaller pieces of material. In this case, the smaller pieces are sand grains.

* Sand is a natural material. Sand is formed through the weathering and erosion of rocks, such as granite, basalt, and limestone. Over time, these rocks break down into smaller particles, which become sand.

So, the process goes like this:

1. Rocks weather and erode into sand.

2. Sand is transported by wind and water.

3. Sand accumulates in layers.

4. Over time, the layers are cemented together by minerals, forming sandstone.