Ruby - Al₂O₃

Ruby, from ruber (latin for red) is the red gem variety of corundum. The red colour is caused by minor amounts of trivalent Cr replacing Al in the crystal structure.

Corundum was named in 1725 by John Woodward and derived from the Sanskrit, kuruvinda ("ruby"). Richard Kirwan used the current spelling "corundum" in 1794. Known by many names in ancient times: adamant, sapphire, ruby, hyacinthos, asteria.

Corundum is a crystalline form of aluminium oxide (Al₂O₃). It is one of the naturally clear transparent materials, but can have different colors when impurities are present. Transparent specimens are used as gems, called ruby if red and padparadscha if pink-orange. All other colors are called sapphire, e.g., "green sapphire" for a green specimen. Corundum occurs as a mineral in mica schist, gneiss, and some marbles in metamorphic terranes. It also occurs in low silica igneous syenite and nepheline syenite intrusives. Other occurrences are as masses adjacent to ultramafic intrusives, associated with lamprophyre dikes and as large crystals in pegmatites.

Optical properties:

• Form Rarely euhedral, usually as small rounded crystals
• Color: Pink
• Pleochroism: From pink to pale pink.
• Relief: High
• Interference colors: Moderate.

Bibliography

• Bucher, K., & Grapes, R. (2011). Petrogenesis of metamorphic rocks. Springer Science & Business Media.
• Fossen, H. (2016). Structural geology. Cambridge University Press.
• Howie, R. A., Zussman, J., & Deer, W. (1992). An introduction to the rock-forming minerals (p. 696). Longman.
• Passchier, Cees W., Trouw, Rudolph A. J: Microtectonics (2005).
• Philpotts, A., & Ague, J. (2009). Principles of igneous and metamorphic petrology. Cambridge University Press.
• 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.
• Vernon, R. H. (2018). A practical guide to rock microstructure. Cambridge university press.

Photo
Chrome-zoisite crystals and big ruby crystal. Anyolite, Tanzania. XPL image, 1x (Field of view = 9mm)	Green chrome-zoisite crystals, pale-green amphibole crystals and big pink ruby crystal. Anyolite, Tanzania. PPL image, 1x (Field of view = 9mm)	Chrome-zoisite crystals, amphibole crystals and ruby crystal. Anyolite, Tanzania. XPL image, 1x (Field of view = 9mm)
Green chrome-zoisite crystals and big pink ruby crystal with brown simplectitic structures. Anyolite, Tanzania. PPL image, 1x (Field of view = 9mm)	Green chrome-zoisite crystals and big pink ruby crystal with brown simplectitic structures. Anyolite, Tanzania. PPL image, 2x (Field of view = 7mm)	Chrome-zoisite crystals and big ruby crystal with brown simplectitic structures. Anyolite, Tanzania. PPL image, 2x (Field of view = 7mm)
Green chrome-zoisite crystals and big pink ruby crystal with brown simplectitic structures. Anyolite, Tanzania. PPL image, 2x (Field of view = 7mm)	Green chrome-zoisite crystals and big pink ruby crystal with brown simplectitic structures. Anyolite, Tanzania. PPL image, 2x (Field of view = 7mm)	Green chrome-zoisite crystals and big pink ruby crystal with brown simplectitic structures. Anyolite, Tanzania. PPL image, 2x (Field of view = 7mm)
Chrome-zoisite crystals and big ruby crystal with brown simplectitic structures. Anyolite, Tanzania. PPL image, 2x (Field of view = 7mm)	Green chrome-zoisite crystals and big pink ruby crystal with brown simplectitic structures. Anyolite, Tanzania. PPL image, 2x (Field of view = 7mm)	Chrome-zoisite crystals and big ruby crystal with brown simplectitic structures. Anyolite, Tanzania. PPL image, 2x (Field of view = 7mm)
Pink ruby crystal with brown simplectitic structures. Anyolite, Tanzania. PPL image, 10x (Field of view = 2mm)	Pink ruby crystal with brown simplectitic structures. Anyolite, Tanzania. XPL image, 10x (Field of view = 2mm)	Pink ruby crystal with brown simplectitic structures. Anyolite, Tanzania. PPL image, 10x (Field of view = 2mm)
Fracture in a pink ruby crystal. Anyolite, Tanzania. PPL image, 10x (Field of view = 2mm)	Fracture in a pink ruby crystal. Anyolite, Tanzania. PPL image, 10x (Field of view = 2mm)	Fracture in a ruby crystal. Anyolite, Tanzania. XPL image, 10x (Field of view = 2mm)

Metamorphic Minerals

Texture and Microstructure

Metamorphic Rocks

Ruby - Al2O3

Ruby - Al₂O₃