Amphibole

Definition

Amphibole is a group of silicate minerals that are characterized by their elongated crystals and double-chain structures. These minerals are significant in geology as they play a critical role in understanding the composition and evolution of igneous and metamorphic rocks. Amphiboles are often dark-colored and can contain various elements like iron, magnesium, and calcium, which contribute to their complex chemistry and physical properties.

5 Must Know Facts For Your Next Test

1. Amphibole minerals can be divided into two main groups: hornblende and tremolite, each with distinct chemical compositions and characteristics.
2. The presence of amphibole in rocks can indicate specific conditions of formation, such as high pressures and temperatures during metamorphism.
3. Amphibole's crystal structure consists of double chains of tetrahedra, which gives it unique physical properties like cleavage at 60° and 120° angles.
4. Common uses of amphibole minerals include their role as indicators of environmental conditions during rock formation and their application in geology for dating rocks.
5. Some amphiboles can pose health risks, such as asbestos-containing varieties, which are known for their fibrous nature and potential for causing lung diseases.

Review Questions

• How do the structural characteristics of amphibole differ from those of pyroxene, and what implications do these differences have for their physical properties?
  • Amphibole has a double-chain structure compared to the single-chain structure of pyroxene. This difference in structure leads to distinct physical properties; for instance, amphiboles typically exhibit cleavage at angles of 60° and 120°, while pyroxenes cleave at 87° and 93°. The elongated crystals of amphibole also allow for different optical properties, affecting how they are identified in rock samples.
• Discuss the significance of amphibole minerals in understanding the processes of metamorphism and the conditions under which they form.
  • Amphibole minerals are crucial indicators of metamorphic processes because their presence signifies specific temperature and pressure conditions. The formation of amphiboles typically occurs during high-grade metamorphism, where rocks undergo significant alteration due to increased heat and pressure. Studying these minerals helps geologists infer the metamorphic history of rocks and the environmental conditions that led to their formation.
• Evaluate the environmental implications associated with amphibole minerals, particularly those containing asbestos, in terms of public health and safety.
  • Amphibole minerals that contain asbestos pose significant environmental and health risks due to their fibrous nature. When disturbed, these fibers can become airborne and inhaled, leading to serious respiratory diseases like asbestosis and mesothelioma. The use of asbestos-containing amphiboles has been heavily regulated or banned in many countries due to these health risks, highlighting the importance of understanding mineral composition not only from a geological perspective but also for public safety.

Related terms

Pyroxene:

A group of important rock-forming silicate minerals that are similar to amphiboles but have a single-chain structure.

Feldspar: The most abundant group of minerals in the Earth's crust, often found in conjunction with amphibole in many igneous rocks.

Metamorphism:

The process by which rocks undergo changes in mineralogy, texture, and chemical composition due to changes in temperature and pressure, often resulting in the formation of amphibole minerals.