Amphibole refers to a significant group of complex silicate minerals, known for their distinct and similar crystal structures and diverse chemical compositions.
Understanding Amphibole: A Mineral Group
At its core, amphibole is the name for a large family of rock-forming minerals. These minerals are categorized together because they share a fundamental "like crystal structure," which is typically characterized by double chains of silicate tetrahedra. This shared structural characteristic gives them similar physical properties, even though their chemical makeup can vary considerably.
- Complex Silicate Minerals: Amphiboles are part of the larger family of silicate minerals, which are the most common minerals in the Earth's crust. They are "complex" because their chemical formulas often include a variety of elements.
Key Chemical Composition
The chemical composition of amphibole minerals is quite varied, but they consistently contain specific metal ions within their structure. They are known to contain a combination of:
- Calcium
- Sodium
- Magnesium
- Aluminum
- Iron
The specific proportions and combinations of these ions lead to the wide range of different amphibole minerals, each with unique properties and appearances.
Pronunciation
The word "amphibole" is pronounced ˈam(p)-fə-ˌbōl.
Characteristics of Amphiboles
Here's a summary of the defining features of this mineral group:
| Characteristic | Description |
|---|---|
| Mineral Type | A group of complex silicate minerals |
| Crystal Structure | Possess like crystal structures, often characterized by double chains |
| Key Elements | Contain calcium, sodium, magnesium, aluminum, and iron ions (or combinations) |
| Common Habit | Often form long, slender, or prismatic crystals |
Common Varieties and Occurrence
Amphiboles are significant components of many igneous and metamorphic rocks. They are found in a wide range of geological settings. Some of the most well-known amphibole minerals include:
- Hornblende: A common, dark-colored amphibole found in many igneous and metamorphic rocks like granite, diorite, and gneiss.
- Tremolite: Often white, gray, or light green, found in metamorphic rocks formed from impure dolomitic limestones.
- Actinolite: A green variety of tremolite, common in greenschist facies metamorphic rocks.
- Crocidolite: A fibrous blue amphibole, notable as one of the forms of asbestos. It's important to note that while some amphiboles (like crocidolite) can occur in fibrous, asbestiform habits, not all amphiboles are asbestos.
Significance
Amphiboles are crucial for geologists in understanding the conditions under which rocks formed, as their specific compositions can indicate pressure, temperature, and chemical environments. Historically, some fibrous forms of amphiboles were used in industrial applications due to their heat resistance and tensile strength, though their use has been largely phased out due to health concerns associated with asbestos.
