Silicon dioxide (SiO2), in the form of sand, is a key ingredient in making bricks, but it's not the only one. Here's why sand is used and how it's used:

* Binder: Sand itself doesn't form a solid brick. It needs a binder to hold the particles together. This binder is usually clay. Clay, when mixed with water and then heated, becomes hard and strong.

* Strength and Durability: Sand provides the structural strength and durability to the brick. It gives the brick its abrasion resistance, making it less likely to break or wear down.

* Porosity: The sand also helps create porosity in the brick. This allows for better insulation and helps the brick to breathe, preventing moisture buildup.

The Process:

1. Clay and sand are mixed with water to form a slurry.

2. This slurry is then molded into the desired brick shape.

3. The bricks are then fired in a kiln at high temperatures.

4. During firing, the clay sinters (melts and solidifies) around the sand particles, creating a strong and durable bond.

So, while silicon dioxide (sand) isn't the primary component that makes up the brick, it plays a crucial role in giving it its strength, durability, and other desired properties.