Final answer:
Hornblende is an amphibole silicate mineral with elongated black crystals commonly found in igneous and metamorphic rocks. It forms a two-chain silicate structure and is an important component of the Earth's crust.
Step-by-step explanation:
Hornblende is a complex silicate, part of a group known as amphiboles. It is typically found in igneous and metamorphic rocks and is recognized by its elongated black crystals.
In silicate minerals, silicon-oxygen tetrahedra can be combined in various structural configurations, including chains, double chains, sheets, and three-dimensional frameworks.
Hornblende forms a two-chain structure with its tetrahedra, which is characteristic of amphibole minerals.
These minerals are commonly found in rocks like granite and in metamorphic rocks such as hornfels, which is formed during contact metamorphism.
Hornblende contributes to the mineral diversity in the Earth's crust and plays a significant role in various geological processes.