Metamorphic Minerals

Texture and Microstructure

Metamorphic Rocks

Hydrogrossular - Ca₃Al₂(SiO₄)_3-x(OH)_4x(x = 0.2-1.5)

Hydrogrossular is a general term for OH-bearing garnet compositions from the grossular-dominant portion of the grossular-katoite series. Hydrogrossular is a calcium aluminium garnet series with formula: Ca₃Al₂(SiO₄)_3-x(OH)_4-x with hydroxide (OH) partially replacing silica SiO₄. The endmembers of the hydrogarnet family (grossular, hibschite, and katoite) depend on the degree of substitution (x):

Grossular: x = 0; Hibschite: 0.2 < x < 1.5; Katoite: 1.5 < x < 3.

Hydrogrossular is a very common mineral in rodingites, in altered gabbroic rocks and in some contact metamorphic rocks.

Optical properties:

• Form: Anhedral masses are common
• Color: Colourless to yellow
• Relief: High
• Interference colors: anomalous first order interference colors

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.

Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 10x (Field of view = 2mm)	Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 2x (Field of view = 7mm)	Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 10x (Field of view = 2mm)
Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 2x (Field of view = 7mm)	Hydrogrossular crystals (with beige color). Montecristo island, Italy. XPL image, 2x (Field of view = 7mm)	Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 2x (Field of view = 7mm)
Hydrogrossular crystals (with beige color). Montecristo island, Italy. XPL image, 2x (Field of view = 7mm)	Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 2x (Field of view = 7mm)	Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 2x (Field of view = 7mm)
Euhedral Hydrogrossular crystal (with beige-green color). Montecristo island, Italy. XPL image, 2x (Field of view = 7mm)	Euhedral Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 2x (Field of view = 7mm)	Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 2x (Field of view = 7mm)
Hydrogrossular crystals (with beige color). Montecristo island, Italy. XPL image, 10x (Field of view = 2mm)	Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 10x (Field of view = 2mm)	Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 10x (Field of view = 2mm)
Hydrogrossular crystals (with beige color). Montecristo island, Italy. XPL image, 2x (Field of view = 7mm)	Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 2x (Field of view = 7mm)	Hydrogrossular crystals (with beige color). Montecristo island, Italy. XPL image, 2x (Field of view = 7mm)
Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 2x (Field of view = 7mm)	Hydrogrossular crystals (with beige color). Montecristo island, Italy. XPL image, 2x (Field of view = 7mm)	Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 2x (Field of view = 7mm)
Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 2x (Field of view = 7mm)	Hydrogrossular crystals (with beige color). Montecristo island, Italy. XPL image, 2x (Field of view = 7mm)	Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 2x (Field of view = 7mm)
Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 2x (Field of view = 7mm)	Hydrogrossular crystals (with beige color). Montecristo island, Italy. XPL image, 10x (Field of view = 2mm)	Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 10x (Field of view = 2mm)
Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 10x (Field of view = 2mm)	Hydrogrossular crystals (with beige color). Montecristo island, Italy. XPL image, 10x (Field of view = 2mm)	Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 10x (Field of view = 2mm)
Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 10x (Field of view = 2mm)	Hydrogrossular crystals (with beige color). Montecristo island, Italy. PPL image, 10x (Field of view = 2mm)	Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 10x (Field of view = 2mm)
Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 10x (Field of view = 2mm)	Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 10x (Field of view = 2mm)	Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 10x (Field of view = 2mm)
Hydrogrossular crystals (with beige color). Montecristo island, Italy. PPL image, 10x (Field of view = 2mm)	Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 10x (Field of view = 2mm)	Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 10x (Field of view = 2mm)
Hydrogrossular crystals (with beige color). Montecristo island, Italy. PPL image, 10x (Field of view = 2mm)	Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 10x (Field of view = 2mm)	Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 10x (Field of view = 2mm)
Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 10x (Field of view = 2mm)	Hydrogrossular crystals (with beige color). Montecristo island, Italy. PPL image, 10x (Field of view = 2mm)	Hydrogrossular crystals (with anomalous first order interference colors). Montecristo island, Italy. XPL image, 10x (Field of view = 2mm)
Zoned hydrogrossular crystals. Capo calamita, Elba island, Italy. PPL image, 2x (Field of view = 7mm)	Zoned hydrogrossular and calcite crystals. Capo calamita, Elba island, Italy. XPL image, 2x (Field of view = 7mm)	Zoned hydrogrossular crystals. Capo calamita, Elba island, Italy. PPL image, 2x (Field of view = 7mm)
Zoned hydrogrossular and calcite crystals. Capo calamita, Elba island, Italy. XPL image, 2x (Field of view = 7mm)	Zoned hydrogrossular crystals. Capo calamita, Elba island, Italy. PPL image, 2x (Field of view = 7mm)	Zoned hydrogrossular and calcite crystals. Capo calamita, Elba island, Italy. XPL image, 10x (Field of view = 2mm)
Zoned hydrogrossular crystals. Capo calamita, Elba island, Italy. PPL image, 2x (Field of view = 7mm)	Zoned hydrogrossular and calcite crystals. Capo calamita, Elba island, Italy. XPL image, 2x (Field of view = 7mm)	Zoned hydrogrossular crystals. Capo calamita, Elba island, Italy. PPL image, 2x (Field of view = 7mm)
Zoned hydrogrossular crystals. Capo calamita, Elba island, Italy. PPL image, 2x (Field of view = 7mm)	Zoned hydrogrossular and calcite crystals. Capo calamita, Elba island, Italy. XPL image, 2x (Field of view = 7mm)	Zoned hydrogrossular crystals. Capo calamita, Elba island, Italy. PPL image, 2x (Field of view = 7mm)
Zoned hydrogrossular crystals. Capo calamita, Elba island, Italy. PPL image, 2x (Field of view = 7mm)	Zoned hydrogrossular and calcite crystals. Capo calamita, Elba island, Italy. XPL image, 2x (Field of view = 7mm)	Zoned hydrogrossular crystals. Capo calamita, Elba island, Italy. PPL image, 10x (Field of view = 2mm)
Zoned hydrogrossular and calcite crystals. Capo calamita, Elba island, Italy. XPL image, 2x (Field of view = 7mm)	Zoned hydrogrossular crystals. Capo calamita, Elba island, Italy. PPL image, 10x (Field of view = 2mm)	Zoned hydrogrossular crystals. Capo calamita, Elba island, Italy. PPL image, 10x (Field of view = 2mm)

Metamorphic Minerals

Texture and Microstructure

Metamorphic Rocks

Hydrogrossular - Ca3Al2(SiO4)3-x(OH)4x(x = 0.2-1.5)

Hydrogrossular - Ca₃Al₂(SiO₄)_3-x(OH)_4x(x = 0.2-1.5)