Amphibole

Definition

Amphibole refers to a group of silicate minerals that share similar crystal structures and chemical compositions, primarily characterized by double chains of silica tetrahedra. These minerals are commonly found in igneous and metamorphic rocks, playing an important role in rock classification and texture, particularly in understanding the mineral composition and formation processes of these rocks.

5 Must Know Facts For Your Next Test

1. Amphiboles are typically dark-colored and can appear in shades ranging from green to black, depending on their specific chemical composition.
2. They are important indicators of the conditions under which igneous and metamorphic rocks form, reflecting aspects like temperature and pressure.
3. The two main types of amphiboles are hornblende and tremolite, each with distinct properties and occurrences in various rock types.
4. Amphiboles can often form through the process of metamorphism when pre-existing minerals undergo changes due to heat and pressure.
5. In terms of crystal structure, amphiboles have a complex arrangement that allows them to form elongated crystals, which is a key feature used for identification.

Review Questions

• How does the presence of amphibole in igneous rocks influence their classification?
  • The presence of amphibole in igneous rocks helps determine their classification by indicating the mineral composition and potential formation conditions. For example, rocks that contain significant amounts of amphibole are often categorized as intermediate to mafic, reflecting a balance between silica content and other minerals. This classification is essential for understanding the geological history and processes that formed the rock.
• Discuss the role of amphibole as a diagnostic mineral in understanding metamorphic processes.
  • Amphibole serves as a diagnostic mineral for identifying specific metamorphic conditions due to its stability range under varying temperature and pressure conditions. The presence of amphiboles like hornblende or tremolite can indicate specific metamorphic environments, such as regional or contact metamorphism. By examining the type and abundance of amphiboles present, geologists can infer the metamorphic history and the conditions under which the rock underwent transformation.
• Evaluate how the chemical composition of amphibole can provide insights into the tectonic environment where igneous rocks were formed.
  • The chemical composition of amphibole can reveal significant information about the tectonic environment in which igneous rocks formed. For instance, variations in the ratios of iron, magnesium, and aluminum within amphibole minerals can suggest whether the rock originated from subduction zones or divergent plate boundaries. By analyzing these compositions, geologists can reconstruct past tectonic settings and understand the geodynamic processes at play during rock formation, linking mineralogy directly to larger geological processes.

Related terms

Pyroxene: A group of silicate minerals that are similar to amphiboles but have a different crystal structure, typically forming single chains of silica tetrahedra.

Felsic: Describes igneous rocks that are rich in feldspar and quartz, often light in color and containing higher amounts of silica, where amphibole can also be present.

Mafic: Refers to igneous rocks that are rich in magnesium and iron, often dark in color, which can also contain amphibole as one of the main mineral constituents.