Buchite

Buchite: A compact, vesicular or slaggy metamorphic rock of any composition containing more than 20% vol. of glass, either produced by contact metamorphism in volcanic to subvolcanic settings or generated by combustion metamorphism. Buchite was named for German mineralogist Baron Christian L. von Buch.

Buchite is an uncommon metamorphic rock type composed mostly of glass, formed by the melting of a sedimentary rock or soil by heat from an adjacent lava flow or scoria eruption, or the burning of an underground coal bed. Buchite is a product of a special type of metamorphism, called pyrometamorphism (contact type, high to very high temperature, low pressure, often connected with coal fires).

Pyrometamorphism: a very high-grade type of contact metamorphism occurring in volcanic settings or around near-surface intrusions and characterised by mineral assemblages stable at or near atmospheric pressure and very high temperatures. Critical minerals are: spurrite, tilleyite, rankinite, larnite and merwinite in silica-deficient carbonate rocks; mullite and glass in aluminous rocks; tridymite and glass in silica-oversaturated rocks.

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Glassy, vesicular buchite. Powder River Basin, northern Wyoming, USA. From James St. John.

Glassy, vesicular buchite. Powder River Basin, northern Wyoming, USA. From James St. John.

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
Acicular pyroxene crystals and rounded quartz crystals embedded in a glassy groundmass. Ardnamurchan, Scotland. PPL image, 2x (Field of view = 7mm)	Acicular pyroxene crystals and rounded quartz crystals embedded in a glassy groundmass. Ardnamurchan, Scotland. PPL image, 2x (Field of view = 7mm)	Acicular pyroxene crystals and rounded quartz crystals embedded in a glassy groundmass. Ardnamurchan, Scotland. PPL image, 2x (Field of view = 7mm)
Acicular pyroxene crystals and rounded quartz crystals embedded in a glassy groundmass. Ardnamurchan, Scotland. PPL image, 10x (Field of view = 2mm)	Acicular pyroxene crystals and rounded quartz crystals embedded in a glassy groundmass. Ardnamurchan, Scotland. PPL image, 10x (Field of view = 2mm)	Acicular pyroxene crystals and skeletal plagioclase (turbid, dirty appearance) crystals embedded in a glassy groundmass. Ardnamurchan, Scotland. PPL image, 10x (Field of view = 2mm)
Acicular pyroxene crystals and skeletal plagioclase crystals embedded in a glassy groundmass. Ardnamurchan, Scotland. PPL image, 10x (Field of view = 2mm)	Acicular pyroxene crystals and skeletal plagioclase (turbid, dirty appearance) crystals embedded in a glassy groundmass. Ardnamurchan, Scotland. PPL image, 10x (Field of view = 2mm)	Acicular pyroxene crystals and skeletal plagioclase crystals embedded in a glassy groundmass. Ardnamurchan, Scotland. PPL image, 10x (Field of view = 2mm)
Acicular pyroxene crystals, rounded quartz and skeletal plagioclase (turbid, dirty appearance) crystals embedded in a glassy groundmass. Ardnamurchan, Scotland. PPL image, 2x (Field of view = 7mm)	Acicular pyroxene crystals, rounded quartz and skeletal plagioclase (turbid, dirty appearance) crystals embedded in a glassy groundmass. Ardnamurchan, Scotland. PPL image, 2x (Field of view = 7mm)	Acicular pyroxene crystals and skeletal plagioclase (turbid, dirty appearance) crystals embedded in a glassy groundmass. Ardnamurchan, Scotland. PPL image, 10x (Field of view = 2mm)
Acicular pyroxene crystals and skeletal plagioclase (turbid, dirty appearance) crystals embedded in a glassy groundmass. Ardnamurchan, Scotland. PPL image, 10x (Field of view = 2mm)	Acicular pyroxene crystals and skeletal plagioclase (turbid, dirty appearance) crystals embedded in a glassy groundmass. Ardnamurchan, Scotland. PPL image, 10x (Field of view = 2mm)	Acicular pyroxene crystals and skeletal plagioclase (turbid, dirty appearance) crystals embedded in a glassy groundmass. Ardnamurchan, Scotland. PPL image, 10x (Field of view = 2mm)