Silica (SiO2) is the most common mineral in the martian crust. The usual form of silica is as Quartz grains, mixed up with other minerals.
Silica is the main component of glass. Glass is a very common construction material, and has a fairly low requirement for embodied energy. Glass is likely to be one of the first in-situ materials produced on Mars.
Silica is produced by mining silica bearing rocks. Rock with a high proportion of silica is crushed until the silica crystals are separated from other minerals. Silica may also be found in windblown formations of sand, where gravity separation processes have separated the fine quartz crystals from other materials.