Phonolitic Scoria

The word scoria comes from the Greek "skoria"= rust; Scoria is a highly vesicular, dark colored volcanic rock that may or may not contain crystals (phenocrysts). It is typically dark in color (generally dark brown, black or purplish red), and basaltic or andesitic in composition. Scoria is relatively low in mass as a result of its numerous macroscopic ellipsoidal vesicles, but in contrast to pumice, all scoria has a specific gravity greater than 1, and sinks in water.

The holes or vesicles form when gases that were dissolved in the magma come out of solution as it erupts, creating bubbles in the molten rock, some of which are frozen in place as the rock cools and solidifies. Scoria may form as part of a lava flow, typically near its surface, or as fragmental ejecta (lapilli, blocks and bombs), for instance in Strombolian eruptions that form steep-sided scoria cones. Most scoria is composed of glassy fragments, and may contain phenocrysts.

scoria.jpg

Basalt-scoria. From nasa.gov



scoria500.jpg

Basalt-scoria. From Neuchatel University, Swiss.



scoria600.jpg

Basalt-scoria. From R.Weller, Cochise College




Bibliography



• David Shelley (1983): Igneous and metamorphic rocks under the microscope. Campman & Hall editori.
• Vernon, R. H. & Clarke, G. L. (2008): Principles of Metamorphic Petrology. Cambridge University Press
• Shelley D (1992): Igneous and Metamorphic Rocks under the Microscope: Classification, textures, microstructures and mineral preferred orientation
• Cox et al. (1979): The Interpretation of Igneous Rocks, George Allen and Unwin, London.
• Eric A.K. (1985): Middlemost Magmas and Magmatic Rocks. Longman, London
• D’Amico C., Innocenti F. & Sassi F.P. (1987): Magmatismo e metamorfismo. UTET
• Innocenti F., Rocchi S. & Triglia R. (1999:) La classificazione delle rocce vulcaniche e subvulcaniche: schema operativo per il progetto CARG.
• Carmichael I.S.E., Turner F.J. & Verghoogen J. (1974): Igneous Petrology. McGraw-Hill.

Photo
scoriafonoliticavulsini(2).jpg

Volcanic vesicle, rounded, white leucite crystals, green pyroxene and brown glass in a Phonolitic scoria from Vulsini, Italy. PPL image, 2x (Field of view = 7mm)
scoriafonoliticavulsini(3).jpg

Volcanic vesicle, rounded, white leucite crystals, green pyroxene and brown glass in a Phonolitic scoria from Vulsini, Italy. PPL image, 2x (Field of view = 7mm)
scoriafonoliticavulsini(4).jpg

Volcanic vesicle, rounded, white leucite crystals, green pyroxene and brown glass in a Phonolitic scoria from Vulsini, Italy. PPL image, 2x (Field of view = 7mm)
scoriafonoliticavulsini(8).jpg

Volcanic vesicle, rounded, white leucite crystals, green pyroxene and brown glass in a Phonolitic scoria from Vulsini, Italy. PPL image, 2x (Field of view = 7mm)
scoriafonoliticavulsini(6).jpg

Volcanic vesicle, rounded, white leucite crystals, green pyroxene and brown glass in a Phonolitic scoria from Vulsini, Italy. PPL image, 2x (Field of view = 7mm)
scoriafonoliticavulsini(7).jpg

Volcanic vesicle, rounded, white leucite crystals, green pyroxene and brown glass in a Phonolitic scoria from Vulsini, Italy. PPL image, 2x (Field of view = 7mm)
scoriafonoliticavulsini(9).jpg

Volcanic vesicle, rounded, white leucite crystals, green pyroxene and brown glass in a Phonolitic scoria from Vulsini, Italy. PPL image, 2x (Field of view = 7mm)