What is the Difference Between Pyroxene and Amphibole?

Pyroxene and amphibole are both types of silicate minerals, but they have distinct differences in their structures and compositions. The main differences between pyroxene and amphibole include:

1. Silicate Structure: Pyroxenes have a single-chain silicate structure, while amphiboles have a double-chain silicate structure.
2. Chemical Composition: Pyroxenes are primarily composed of single-chain silicate tetrahedra, while amphiboles contain double-chain silicate tetrahedra.
3. Crystal Shapes: In general, pyroxene crystals tend to be stubbier than the more elongated amphibole crystals.
4. Cleavage: The best way to distinguish between pyroxenes and amphiboles is by the angle between cleavage planes. Pyroxene cleavage faces tend to meet at nearly right angles, while amphibole cleavage faces meet at angles of nearly 60 degrees and 120 degrees.
5. Cross-sections: When looking down the long axis of a cleavage fragment, pyroxenes have rectangular cross-sections, while amphiboles exhibit a diamond- or wedge-shaped pattern.
6. Fracture/Cleavage: Amphiboles, like hornblende, tend to have a more splintery fracture/cleavage than pyroxenes.

Some common examples of pyroxene minerals include augite and diopside, while amphibole minerals include hornblende, actinolite, and tremolite.

Comparative Table: Pyroxene vs Amphibole

The main difference between pyroxene and amphibole lies in their silicate structures. Pyroxene is a single-chain inosilicate, while amphibole is a double-chain inosilicate. Here is a comparison table highlighting the differences between pyroxene and amphibole:

It is important not to use the terms pyroxene and amphibole interchangeably, as their distinct differences in physical and chemical properties can lead to misidentification of rocks and minerals, which can have significant implications in geologic studies and exploration.