Silica tetrahedral unit is an essential component of minerals and rocks. It is made up of four oxygen atoms surrounding a silicon atom, forming a tetrahedron. In this unit, the silicon structure is enclosed by oxygen atoms.

Explanation:

Silica tetrahedral unit is the building block of silicate minerals, which are the most abundant minerals on earth. It is composed of a single silicon atom (Si) at the center of the tetrahedron and four oxygen atoms (O) located at the vertices of the tetrahedron. The chemical formula of the silica tetrahedron is SiO4.

The silicon atom in the tetrahedron has a valency of four, which means it can form bonds with four oxygen atoms. The oxygen atoms, on the other hand, have a valency of two, which means they can form bonds with two other atoms. Thus, each oxygen atom in the tetrahedron is shared by two neighboring tetrahedra, forming a three-dimensional network of linked tetrahedra.

The silica tetrahedral unit is enclosed by oxygen atoms, which form strong covalent bonds with the silicon atom. These bonds are responsible for the high stability and hardness of silicate minerals. The tetrahedral structure also gives the minerals their characteristic physical and chemical properties, such as cleavage, hardness, density, and chemical reactivity.

In conclusion, the silicon structure in the silica tetrahedral unit is enclosed by oxygen atoms, which form a three-dimensional network of linked tetrahedra. This structural arrangement is responsible for the unique properties and abundance of silicate minerals.