Orthopyroxene - XYZ₂O₆

Optical properties:

• Colour and Pleochroism: Colourless
• Form: crystals form stubby prisms elongate along the c-axis, basal sections are 4 or 8 sided and show two cleavages at 90°
• Cleavage: typical pyroxene cleavages parallel to {110}, which intersect at ~90°
• Twinning: simple and lamellar twins and composition planes, which in combination may form a herringbone pattern
• Alteration: commonly alter to uralite (a light coloured amphibole), or may alter to serpentine, chlorite, biotite, carbonates and /or other silicates
• Relief: high positive
• Distinguishing Features: low interference colors, straigth extinction.

Bibliography

• Cox et al. (1979): The Interpretation of Igneous Rocks, George Allen and Unwin, London.
• Howie, R. A., Zussman, J., & Deer, W. (1992). An introduction to the rock-forming minerals (p. 696). Longman.
• Le Maitre, R. W., Streckeisen, A., Zanettin, B., Le Bas, M. J., Bonin, B., Bateman, P., & Lameyre, J. (2002). Igneous rocks. A classification and glossary of terms, 2. Cambridge University Press.
• Middlemost, E. A. (1986). Magmas and magmatic rocks: an introduction to igneous petrology.
• Shelley, D. (1993). Igneous and metamorphic rocks under the microscope: classification, textures, microstructures and mineral preferred-orientations.
• Vernon, R. H. & Clarke, G. L. (2008): Principles of Metamorphic Petrology. Cambridge University Press.

photo
Orthopyroxene crystal in a dacite. XPL image , 10x (Field of view = 2mm)	Orthopyroxene crystal in a dacite. XPL image , 10x (Field of view = 2mm)	Orthopyroxene crystal in a dacite. PPL image , 10x (Field of view = 2mm)
Orthopyroxene crystal with clinopyroxene rim in a dacite. XPL image , 10x (Field of view = 2mm)	Orthopyroxene crystal with clinopyroxene rim in a dacite. XPL image , 10x (Field of view = 2mm)	Orthopyroxene crystal. PPL image , 10x (Field of view = 2mm)
Orthopyroxene crystal with clinopyroxene rim in a dacite. XPL image , 10x (Field of view = 2mm)	Orthopyroxene crystal with clinopyroxene rim in a dacite. XPL image , 10x (Field of view = 2mm)	Orthopyroxene crystal with clinopyroxene rim in a dacite. XPL image , 10x (Field of view = 2mm)
Orthopyroxene crystal. PPL image , 2x (Field of view = 7mm)	Orthopyroxene crystal. XPL image , 2x (Field of view = 7mm)	Orthopyroxene crystal. XPL image , 2x (Field of view = 7mm)
Orthopyroxene crystal. XPL image , 10x (Field of view = 2mm)