Difference Between Pyroxene and Amphibole

The key difference between pyroxene and amphibole is that the pyroxene is a form of inosilicate, which contains single chains of SiO₃ tetrahedra whereas the amphibole is a form of inosilicate, which contains double chain SiO₄ tetrahedra.

Inosilicates are a form of silicate minerals. We call them “chain silicates” as well. These minerals have interlocking chains of silicate tetrahedra with either SiO₃ or Si₄O₁₁. There are two major groups of inosilicates according to the number of chains present in the mineral. They are pyroxene group minerals and amphibole group minerals.

CONTENTS

1. Overview and Key Difference
2. What is Pyroxene
3. What is Amphibole
4. Side by Side Comparison – Pyroxene vs Amphibole in Tabular Form
5. Summary

What is Pyroxene?

The term pyroxene refers to any of a large class of rock-forming silicate minerals, generally containing calcium, magnesium, and iron and typically occurring as prismatic crystals. It is one of the two groups of inosilicates or chain silicates. Unlike the amphibole group, this group is a single chain inosilicate. This is because these minerals consist of single chains of SiO₃ tetrahedra.

The minerals of this group occur in igneous and metamorphic rocks. The general chemical formula of these minerals is XY(Si,Al)₂O₆ in which the “X” indicates calcium, sodium, iron(+2) or magnesium and “Y” indicates chromium, aluminium, iron(+3), cobalt, titanium and many other metals with comparatively a small size. According to the crystal system, there are two types of pyroxenes.

1. Clinopyroxenes – crystallize in the monoclinic system.
2. Orthopyroxenes – crystallize in the orthorhombic system.

Some examples for pyroxene minerals include aegirine, augite, clinoenstatite, diopside, jadeite, etc.

What is Amphibole?

The term amphibole refers to any of a large class of inosilicate minerals containing iron or magnesium or both. These minerals occur as either prism or needle-like crystals, containing double chain SiO₄ tetrahedra; thus, we name them as double chain inosilicates. We may find these minerals in nature in various colors such as green, black, colorless, white, yellow, blue, or brown. Therefore, we can find these minerals naturally in either igneous or metamorphic rocks.

There are two forms of crystal structures we can see among these minerals. They are the monoclinic crystal structure and the orthorhombic crystal structure. In their general characteristic, they are similar to pyroxenes but are different in some aspects. As the main difference between these two groups, amphiboles essentially contain hydroxyl (OH-) or halogen groups (such as F and Cl). Some common examples of amphibole minerals include anthophyllite, holmquistite, ferrogedrite, tremolite, etc.

What is the Difference Between Pyroxene and Amphibole?

The term pyroxene refers to any of a large class of rock-forming silicate minerals, generally containing calcium, magnesium, and iron and typically occurring as prismatic crystals. They fall into the category of single chain inosilicates. This is mainly because these minerals contain single chains of SiO₃ tetrahedra. The term amphibole refers to any of a large class of inosilicate minerals containing iron or magnesium or both. They fall into the category of double chain inosilicates because they contain double chain SiO₄ tetrahedra. Moreover, Pyroxene may or may not contain hydroxyl or halogen groups while Amphiboles essentially contain hydroxyl (OH-) or halogen groups (such as F and Cl). The below infographic presents more details on the difference between pyroxene and amphibole in tabular form.

Summary – Pyroxene vs Amphibole

Pyroxene and amphiboles are two forms of silicate minerals that differ from each other mainly according to their chemical structure. The difference between pyroxene and amphibole is that the pyroxene is a form of inosilicate which contains single chains of SiO₃ tetrahedra whereas the amphibole is a form of inosilicate which contains double chain SiO₄ tetrahedra.

Reference:

1. “Pyroxene.” Wikipedia, Wikimedia Foundation, 5 July 2018. Available here
2. “Amphibole.” Wikipedia, Wikimedia Foundation, 14 Aug. 2018. Available here  

Image Courtesy:

1.”Tremolite-121232″By Rob Lavinsky, iRocks.com (CC BY-SA 3.0) via Commons Wikimedia  
2.”Diopside-172005″By Rob Lavinsky, iRocks.com (CC BY-SA 3.0) via Commons Wikimedia