Pseudomorph

Pseudomorph is a mineral formed by chemical or structural change of another substance, though retaining its original external shape. Although pseudomorphs give the appearance of being crystalline, they are commonly granular and waxy internally and have no regular cleavage; those that are crystalline have optical properties different from those required by their outward form. The name literally means "false form".

Pseudomorphs are formed by substitution, deposition, or alteration:

• In the formation of a pseudomorph by substitution, the original substance has been gradually removed and simultaneously replaced by another. A common example of this is petrified wood, in which all the cellulose fibres have been replaced by silica, even those in the bark.

• Pseudomorphs can be formed by deposition of one mineral on the surface of crystals of another.

• Alteration pseudomorphs may be formed in several ways: from a change in internal crystal structure without a change in chemical composition (these pseudomorphs are called paramorphs; e.g., aragonite becomes calcite, and brookite becomes rutile); by the loss of an ingredient from the original compound (e.g., cuprite loses oxygen to form copper); by the addition of an ingredient to the original compound (e.g., anhydrite adds water to form gypsum, and cuprite adds carbon dioxide and water to form malachite); and by an exchange of constituents (e.g., feldspar loses potassium silicate and gains water to become kaolinite).

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
Garnet pseudomorphed by chlorite. XPL image, 10x (Field of view = 2mm)	Garnet pseudomorphed by chlorite. XPL image, 10x (Field of view = 2mm)	Garnet pseudomorphed by chlorite. PPL image, 10x (Field of view = 2mm)
Garnet pseudomorphed by chlorite. PPL image, 10x (Field of view = 2mm)	Garnet pseudomorphed by chlorite. XPL image, 10x (Field of view = 2mm)	Garnet pseudomorphed by chlorite. XPL image, 10x (Field of view = 2mm)
Garnet partially pseudomorphed by chlorite. PPL image, 2x (Field of view = 7mm)	Garnet partially pseudomorphed by chlorite. PPL image, 2x (Field of view = 7mm)	Garnet partially pseudomorphed by chlorite. XPL image, 2x (Field of view = 7mm)
Garnet partially pseudomorphed by chlorite. PPL image, 2x (Field of view = 7mm)	Garnet partially pseudomorphed by chlorite. PPL image, 2x (Field of view = 7mm)	Garnet partially pseudomorphed by chlorite. XPL image, 2x (Field of view = 7mm)
Garnet partially pseudomorphed by chlorite. PPL image, 2x (Field of view = 7mm)	Garnet pseudomorphed by chlorite. PPL image, 2x (Field of view = 7mm)	Garnet pseudomorphed by chlorite. XPL image, 2x (Field of view = 7mm)
Garnet crystals partially pseudomorphed by chlorite; glaucophane (blu) and Epidote (pale yellow) in a bluschist from Jenner, California, USA. PPL image, 1x (Field of view = 9mm)	Garnet crystals partially pseudomorphed by chlorite; glaucophane and Epidote in a bluschist from Jenner, California, USA. XPL image, 1x (Field of view = 9mm)	Garnet crystal partially pseudomorphed by chlorite; glaucophane (blu) and Epidote (pale yellow) in a bluschist from Jenner, California, USA. PPL image, 2x (Field of view = 7mm)
Garnet crystal partially pseudomorphed by chlorite; glaucophane (blu) and Epidote (pale yellow) in a bluschist from Jenner, California, USA. PPL image, 2x (Field of view = 7mm)	Garnet crystals partially pseudomorphed by chlorite; glaucophane (blu) and Epidote (pale yellow) in a bluschist from Jenner, California, USA. PPL image, 2x (Field of view = 7mm)	Garnet crystals partially pseudomorphed by chlorite; glaucophane and Epidote in a bluschist from Jenner, California, USA. XPL image, 2x (Field of view = 7mm)
Garnet crystal partially pseudomorphed by chlorite; glaucophane (blu) and Epidote (pale yellow) in a bluschist from Jenner, California, USA. PPL image, 2x (Field of view = 7mm)	Garnet crystal partially pseudomorphed by chlorite; glaucophane (blu) and Epidote (pale yellow) in a bluschist from Jenner, California, USA. PPL image, 2x (Field of view = 7mm)	Garnet crystal partially pseudomorphed by chlorite; glaucophane (blu) and Epidote (pale yellow) in a bluschist from Jenner, California, USA. PPL image, 2x (Field of view = 7mm)