Example of a three-dimensional silicate is:

First, let's understand what a three-dimensional silicate is. Silicates are minerals composed of silicon and oxygen atoms. The basic building block is the SiO₄ tetrahedron, where a silicon atom is surrounded by four oxygen atoms. These tetrahedra can link together in different ways to form various structures.

In three-dimensional silicates, the SiO₄ tetrahedra are connected in all three spatial directions, forming a continuous network. This type is also called tectosilicates or framework silicates. Each oxygen atom is shared between two silicon atoms, creating a rigid 3D structure.

Now, let's examine each option:

Option A: Ultramarines

Ultramarines are minerals like lapis lazuli. They are complex aluminosilicates with a sodalite cage structure. In this structure, SiO₄ and AlO₄ tetrahedra are interconnected in three dimensions, forming a framework. Therefore, ultramarines are three-dimensional silicates.

Option B: Feldspars

Feldspars are common rock-forming minerals (e.g., orthoclase, albite). They are aluminosilicates where SiO₄ and AlO₄ tetrahedra share all their oxygen atoms to build an extensive 3D network. This qualifies feldspars as three-dimensional silicates.

Option C: Zeolites

Zeolites are microporous aluminosilicates (e.g., natrolite). They have a honeycomb-like 3D framework where SiO₄ and AlO₄ tetrahedra are linked in all directions, creating channels and cavities. Thus, zeolites are also three-dimensional silicates.

Since ultramarines (A), feldspars (B), and zeolites (C) all exhibit three-dimensional silicate structures, the correct choice is "All of these."

Hence, the correct answer is Option D.