Amphibole

Definition

Amphibole refers to a group of inosilicate minerals characterized by double chains of silica tetrahedra. These minerals are significant in the context of various geological processes, particularly in the formation of igneous and metamorphic rocks, due to their presence in a range of rock types and their role in crystallization and mineral stability.

5 Must Know Facts For Your Next Test

1. Amphiboles are typically dark-colored minerals that can include varieties such as hornblende and tremolite, commonly found in metamorphic rocks.
2. The crystal structure of amphibole allows for the inclusion of various cations like iron, magnesium, and calcium, giving rise to a range of physical properties.
3. Amphiboles play an important role in the geological cycle as they can form under high-pressure conditions in subduction zones, influencing the mineralogy of volcanic rocks.
4. These minerals have perfect cleavage in two directions at angles of 60° and 120°, which is a key identifying feature when studying rock samples.
5. Amphibole minerals can also contribute to environmental processes, including the weathering of rocks and the cycling of elements such as magnesium and iron.

Review Questions

• How do the structural characteristics of amphibole minerals influence their formation and occurrence in igneous and metamorphic rocks?
  • The structural characteristics of amphibole minerals, specifically their double chain arrangement of silica tetrahedra, play a crucial role in their formation within igneous and metamorphic environments. This unique structure allows amphiboles to stabilize under high temperatures and pressures, making them common in mafic to intermediate volcanic rocks as well as high-grade metamorphic rocks. Their ability to incorporate various cations also influences their occurrence and stability in different geological settings.
• Compare the properties and occurrences of amphibole and pyroxene minerals, emphasizing their differences in rock formation contexts.
  • Amphibole and pyroxene are both important inosilicate mineral groups with chain structures but differ significantly in their formation contexts and properties. Amphiboles have a double chain structure that allows them to form in more hydrous environments, typically found in metamorphic rocks or certain igneous rocks. In contrast, pyroxenes have a single chain structure and are often found in basaltic lavas and some intrusive igneous rocks. Their differing crystallization behaviors lead to distinct mineralogical compositions depending on the specific geological environment.
• Evaluate the environmental implications of amphibole weathering processes on ecosystem health and element cycling.
  • The weathering processes involving amphibole minerals can significantly impact ecosystem health and element cycling. As amphiboles weather, they release essential nutrients like magnesium and iron into the soil and water systems, promoting plant growth and influencing aquatic ecosystems. Additionally, the breakdown of these minerals can affect soil composition and pH levels, impacting biodiversity. Understanding these processes is crucial for assessing ecological balance and environmental restoration efforts, especially in regions affected by mining or natural disturbances.

Related terms

Inosilicates: A class of silicate minerals that includes chains of tetrahedra, characterized by their structural arrangement, which can be single or double chains.

Pyroxene: Another group of silicate minerals that, like amphiboles, have chain structures but are distinguished by their single chain formation and different crystal habits.

Mica: A group of phyllosilicate minerals known for their sheet-like structure, often found in association with amphibole in metamorphic rocks.