Amphibole vs. Pyroxene

Attribute	Amphibole	Pyroxene
Chemical Formula	Complex silicate minerals	Simple silicate minerals
Crystal System	Monoclinic	Monoclinic or Orthorhombic
Color	Varies (commonly dark green, black, or brown)	Varies (commonly dark green, black, or brown)
Cleavage	Two directions at approximately 60 and 120 degrees	Two directions at approximately 90 degrees
Hardness	5-6 on Mohs scale	5-6 on Mohs scale
Luster	Vitreous to dull	Vitreous to dull
Streak	White	White
Specific Gravity	2.9-3.6	3.2-4.0
Occurrences	Common in metamorphic rocks	Common in igneous rocks
Uses	Asbestos, construction materials, gemstones	Construction materials, gemstones

Introduction

Amphibole and pyroxene are two major groups of rock-forming minerals that are commonly found in igneous and metamorphic rocks. While they share some similarities, they also have distinct characteristics that set them apart. In this article, we will explore the attributes of amphibole and pyroxene, including their crystal structures, chemical compositions, physical properties, and geological occurrences.

Crystal Structure

Amphibole and pyroxene have different crystal structures. Amphibole minerals belong to the double-chain silicate group, characterized by two chains of tetrahedra linked together by metal cations. This structure gives amphiboles a prismatic or needle-like shape. On the other hand, pyroxene minerals belong to the single-chain silicate group, where the tetrahedral chains are not linked. This results in a more blocky or stubby crystal shape for pyroxenes.

Chemical Composition

Amphibole and pyroxene also differ in their chemical compositions. Amphiboles are complex minerals with a wide range of chemical compositions. They typically contain elements such as silicon, oxygen, aluminum, iron, magnesium, calcium, sodium, and potassium. The specific combination of these elements determines the different types of amphiboles, such as hornblende, actinolite, and tremolite. On the other hand, pyroxenes have a simpler chemical composition, mainly consisting of silicon, oxygen, and metal cations such as iron, magnesium, calcium, and sodium. Common types of pyroxenes include augite, diopside, and enstatite.

Physical Properties

When it comes to physical properties, amphibole and pyroxene exhibit some similarities but also have distinct characteristics. Both minerals have a hardness of around 5 to 6 on the Mohs scale, making them relatively hard. However, amphiboles tend to be slightly softer than pyroxenes. In terms of color, amphiboles can range from colorless to various shades of green, brown, and black, while pyroxenes are typically dark-colored, ranging from greenish-black to black. Amphiboles also have a prismatic cleavage, meaning they break along distinct planes, while pyroxenes have a cleavage that is less pronounced and more irregular.

Geological Occurrences

Amphibole and pyroxene minerals are commonly found in different geological settings. Amphiboles are often associated with intermediate to felsic igneous rocks, such as granites and diorites, as well as metamorphic rocks like schists and gneisses. They can also occur in hydrothermal veins and as accessory minerals in some ore deposits. Pyroxenes, on the other hand, are more commonly found in mafic and ultramafic igneous rocks, such as basalt and peridotite. They are also present in some metamorphic rocks, particularly those formed under high-pressure conditions. Additionally, pyroxenes can be found in meteorites and lunar samples.

Uses

Both amphibole and pyroxene minerals have various uses in different industries. Amphiboles, particularly the variety known as asbestos, were widely used in the past for their heat resistance and insulating properties. However, due to the health risks associated with asbestos fibers, its use has been heavily regulated or banned in many countries. Non-asbestos varieties of amphiboles are still used in some applications, such as in the production of ceramics and as a filler in certain plastics. Pyroxenes, on the other hand, have limited industrial uses. Some varieties, like diopside, are used as gemstones, while others are used in the production of refractory materials and as a source of iron and magnesium in the steel industry.

Conclusion

In conclusion, amphibole and pyroxene minerals are important components of many rocks and have distinct attributes that differentiate them from each other. While both minerals have different crystal structures, chemical compositions, physical properties, and geological occurrences, they play significant roles in the formation and composition of various rock types. Understanding the characteristics of amphibole and pyroxene minerals is crucial for geologists and mineralogists in identifying and interpreting rocks and their geological history.